SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549



                                  SCHEDULE 13D
                                 (Rule 13d-101)

  INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT TO RULE 13d-1(A) AND
               AMENDMENTS THERETO FILED PURSUANT TO RULE 13d-2(a)

                            (Amendment No. _______)1



                             Siga Technologies, Inc.
                           ---------------------------
                                (Name of Issuer)

                    Common Stock, par value $.0001 per share
                    ----------------------------------------
                         (Title of Class of Securities)

                                  82 6917-10-6
                                  ------------
                                 (CUSIP Number)

                                Donald G. Drapkin
                               35 East 62nd Street
                               New York, NY 10021
                                 (212) 872-0012

                                 with a copy to:

                       Kramer Levin Naftalis & Frankel LLP
                                919 Third Avenue
                               New York, NY 10022
                            Attn: Thomas E. Constance
                                 (212) 715-9100

   (Name, Address and Telephone Number of Person Authorized to Receive Notices
                               and Communications)

                                 March 30, 2001
                                 --------------
             (Date of Event which Requires Filing of this Statement)

      If the filing person has previously filed a statement on Schedule 13G to
report the acquisition which is the subject of this Schedule 13D, and is filing
this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the
following box [x]

            Note: Schedules filed in paper format shall include a signed
      original and five copies of the schedule, including all exhibits. See Rule
      13d-7 for other parties to whom copies are to be sent.

                         (Continued on following pages)

                              (Page 1 of 13 Pages)


- -----------------------

1        The  remainder  of this cover page shall be filled out for a  reporting
person's  initial  filing on this  form with  respect  to the  subject  class of
securities,  and for any subsequent amendment containing information which would
alter disclosures provided in a prior cover page.

         The information  required on the remainder of this cover page shall not
be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange
Act of 1934 ("Act") or otherwise  subject to the  liabilities of that section of
the Act but shall be subject to all other  provisions of the Act  (however,  see
the Notes).



- --------------------------------------------------------------------------------
                                        13D                   Page 2 of 13 Pages
    CUSIP No. 82 6917-10-6
- --------------------------------------------------------------------------------
    1     NAMES OF REPORTING PERSONS
          I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)

          Donald G. Drapkin
- --------------------------------------------------------------------------------
    2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*     (a) [ ]
                                                                (b) [x]
- --------------------------------------------------------------------------------
    3     SEC USE ONLY

- --------------------------------------------------------------------------------
    4     SOURCE OF FUNDS*
          PF, OO (see Item 3)
- --------------------------------------------------------------------------------
    5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEM 2(d) or 2(e)
                                                                        [  ]
- --------------------------------------------------------------------------------
    6     CITIZENSHIP OR PLACE OF ORGANIZATION
          United States
- --------------------------------------------------------------------------------
          NUMBER OF               7     SOLE VOTING POWER
            SHARES                      1,279,032** ***
         BENEFICIALLY         --------------------------------------------------
        OWNED BY EACH             8     SHARED VOTING POWER
          REPORTING                     11,750 ***
         PERSON WITH          --------------------------------------------------
                                  9     SOLE DISPOSITIVE POWER
                                        373,400***
                              --------------------------------------------------
                                  10    SHARED DISPOSITIVE POWER
                                        11,750 ***
- --------------------------------------------------------------------------------
   11     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          1,290,282** ***
- --------------------------------------------------------------------------------
   12     CHECK BOX IF THE AGGREGATE  AMOUNT IN ROW 11 EXCLUDES  CERTAIN SHARES*
          **
                                                                  [x]
- --------------------------------------------------------------------------------
   13     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
          17.3%** ***
- --------------------------------------------------------------------------------
   14     TYPE OF REPORTING PERSON*
          IN
- --------------------------------------------------------------------------------
                      *SEE INSTRUCTIONS BEFORE FILLING OUT

** Mr. Drapkin has entered into a Management Restructuring Agreement (see Item
4), pursuant to which, he will be granted proxies giving him voting power over
an aggregate of 905,632 shares of Common Stock.

*** Mr. Drapkin holds, inter alia, (i) a warrant (an "Investor Warrant") to
purchase 347,826 shares of Common Stock and (ii) Debentures, the principal and
accrued interest on which as of January 31, 2001 were convertible into an
aggregate of approximately 368,696 shares of Common Stock. However, the
Debentures and the Investor Warrant each provides that, with certain limited
exceptions, they are not convertible or exercisable, as the case may be, if, as
a result of such action, the number of shares of Common Stock beneficially owned
by Mr. Drapkin and his affiliates (other than shares of Common Stock which may
be deemed beneficially owned through the ownership of the unexercised portion of
such securities) would exceed 9.99% of the outstanding shares of Common Stock.
As a result of the restrictions described in the immediately preceding sentence
and the other securities which Mr. Drapkin may be deemed beneficially to own, as
of April 6, 2001, Mr. Drapkin's Debentures and Investor Warrant are not
presently convertible or exercisable.



- --------------------------------------------------------------------------------
                                           13D                Page 3 of 13 Pages
    CUSIP No. 82 6917-10-6
- --------------------------------------------------------------------------------
    1     NAMES OF REPORTING PERSONS
          I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)

          Drapkin Family Charity Foundation
- --------------------------------------------------------------------------------
    2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*           (a) [ ]
                                                                      (b) [x]
- --------------------------------------------------------------------------------
    3     SEC USE ONLY

- --------------------------------------------------------------------------------
    4     SOURCE OF FUNDS*
          OO (see Item 3)
- --------------------------------------------------------------------------------
    5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEM 2(d) or 2(e)
                                                                      [  ]
- --------------------------------------------------------------------------------
    6     CITIZENSHIP OR PLACE OF ORGANIZATION
          New Jersey
- --------------------------------------------------------------------------------
          NUMBER OF               7     SOLE VOTING POWER
            SHARES                      0
         BENEFICIALLY         --------------------------------------------------
        OWNED BY EACH             8     SHARED VOTING POWER
          REPORTING                     11,750
         PERSON WITH          --------------------------------------------------
                                  9     SOLE DISPOSITIVE POWER
                                        0
                              --------------------------------------------------
                                  10    SHARED DISPOSITIVE POWER
                                        11,750
- --------------------------------------------------------------------------------
   11     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          11,750
- --------------------------------------------------------------------------------
   12     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 11 EXCLUDES CERTAIN SHARES*
                                                                      [  ]
- --------------------------------------------------------------------------------
   13     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
          0.2%
- --------------------------------------------------------------------------------
   14     TYPE OF REPORTING PERSON*
          00 (see Item 2)
- --------------------------------------------------------------------------------
                      *SEE INSTRUCTIONS BEFORE FILLING OUT



- --------------------------------------------------------------------------------
                                             13D             Page 4 of 13 Pages
    CUSIP No. 82 6917-10-6
- --------------------------------------------------------------------------------
    1     NAMES OF REPORTING PERSONS
          I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)

          Gabriel M. Cerrone
- --------------------------------------------------------------------------------
    2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*     (a) [ ]
                                                                (b) [x]
- --------------------------------------------------------------------------------
    3     SEC USE ONLY

- --------------------------------------------------------------------------------
    4     SOURCE OF FUNDS*
          PF, OO (see Item 3)
- --------------------------------------------------------------------------------
    5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEM 2(d) or 2(e)
                                                                    [  ]
- --------------------------------------------------------------------------------
    6     CITIZENSHIP OR PLACE OF ORGANIZATION
          United States
- --------------------------------------------------------------------------------
          NUMBER OF               7     SOLE VOTING POWER
            SHARES                      0
         BENEFICIALLY         --------------------------------------------------
        OWNED BY EACH             8     SHARED VOTING POWER
          REPORTING                     574,700 **
         PERSON WITH          --------------------------------------------------
                                  9     SOLE DISPOSITIVE POWER
                                        0
                              --------------------------------------------------
                                  10    SHARED DISPOSITIVE POWER
                                        574,700 **
- --------------------------------------------------------------------------------
   11     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          574,700 **
- --------------------------------------------------------------------------------
   12     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 11 EXCLUDES CERTAIN SHARES*
                                                                      [  ]
- --------------------------------------------------------------------------------
   13     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
          7.2%
- --------------------------------------------------------------------------------
   14     TYPE OF REPORTING PERSON*
          IN
- --------------------------------------------------------------------------------
                      *SEE INSTRUCTIONS BEFORE FILLING OUT

**    Mr. Cerrone, as the sole general partner of Panetta Partners Ltd., may
be deemed beneficially to own the securities held by Panetta.



- --------------------------------------------------------------------------------
                                             13D              Page 5 of 13 Pages
    CUSIP No. 82 6917-10-6
- --------------------------------------------------------------------------------
    1     NAMES OF REPORTING PERSONS
          I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)

          Panetta Partners Ltd.
- --------------------------------------------------------------------------------
    2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*     (a) [ ]
                                                                (b) [x]
- --------------------------------------------------------------------------------
    3     SEC USE ONLY

- --------------------------------------------------------------------------------
    4     SOURCE OF FUNDS*
          OO (see Item 3)
- --------------------------------------------------------------------------------
    5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEM 2(d) or 2(e)
                                                                       [  ]
- --------------------------------------------------------------------------------
    6     CITIZENSHIP OR PLACE OF ORGANIZATION
          Colorado
- --------------------------------------------------------------------------------
          NUMBER OF               7     SOLE VOTING POWER
            SHARES                      0
         BENEFICIALLY          -------------------------------------------------
        OWNED BY EACH             8     SHARED VOTING POWER
          REPORTING                     574,700
         PERSON WITH           -------------------------------------------------
                                  9     SOLE DISPOSITIVE POWER
                                        0
                               -------------------------------------------------
                                  10    SHARED DISPOSITIVE POWER
                                        574,700
- --------------------------------------------------------------------------------
   11     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          574,700
- --------------------------------------------------------------------------------
   12     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 11 EXCLUDES CERTAIN SHARES*
                                                                       [  ]
- --------------------------------------------------------------------------------
   13     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
          7.2%
- --------------------------------------------------------------------------------
   14     TYPE OF REPORTING PERSON*
          PN
- --------------------------------------------------------------------------------



- --------------------------------------------------------------------------------
                                             13D             Page 6 of 13 Pages
    CUSIP No. 82 6917-10-6
- --------------------------------------------------------------------------------
    1     NAMES OF REPORTING PERSONS
          I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)

          Thomas E. Constance
- --------------------------------------------------------------------------------
    2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*     (a) [ ]
                                                                (b) [x]
- --------------------------------------------------------------------------------
    3     SEC USE ONLY

- --------------------------------------------------------------------------------
    4     SOURCE OF FUNDS*
          N/A
- --------------------------------------------------------------------------------
    5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEM 2(d) or 2(e)
                                                                       [  ]
- --------------------------------------------------------------------------------
    6     CITIZENSHIP OR PLACE OF ORGANIZATION
          United States
- --------------------------------------------------------------------------------
          NUMBER OF               7     SOLE VOTING POWER
            SHARES                      0
         BENEFICIALLY         --------------------------------------------------
        OWNED BY EACH             8     SHARED VOTING POWER
          REPORTING                     0
         PERSON WITH          --------------------------------------------------
                                  9     SOLE DISPOSITIVE POWER
                                        0
                              --------------------------------------------------
                                  10    SHARED DISPOSITIVE POWER
                                        0
- --------------------------------------------------------------------------------
   11     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          0
- --------------------------------------------------------------------------------
   12     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 11 EXCLUDES CERTAIN SHARES*
                                                                    [  ]
- --------------------------------------------------------------------------------
   13     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
          0.0%
- --------------------------------------------------------------------------------
   14     TYPE OF REPORTING PERSON*
          IN
- --------------------------------------------------------------------------------
                      *SEE INSTRUCTIONS BEFORE FILLING OUT



- --------------------------------------------------------------------------------
                                             13D              Page 7 of 13 Pages
    CUSIP No. 82 6917-10-6
- --------------------------------------------------------------------------------
    1     NAMES OF REPORTING PERSONS
          I.R.S. IDENTIFICATION NO. OF ABOVE PERSON (ENTITIES ONLY)

          Eric A. Rose, M.D.
- --------------------------------------------------------------------------------
    2     CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*           (a) [  ]
                                                                (b) [x]
- --------------------------------------------------------------------------------
    3     SEC USE ONLY

- --------------------------------------------------------------------------------
    4     SOURCE OF FUNDS*
          N/A
- --------------------------------------------------------------------------------
    5     CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO
          ITEM 2(d) or 2(e)
                                                                          [  ]
- --------------------------------------------------------------------------------
    6     CITIZENSHIP OR PLACE OF ORGANIZATION
          United States
- --------------------------------------------------------------------------------
          NUMBER OF               7     SOLE VOTING POWER
            SHARES                      0
         BENEFICIALLY          -------------------------------------------------
        OWNED BY EACH             8     SHARED VOTING POWER
          REPORTING                     0
         PERSON WITH           -------------------------------------------------
                                  9     SOLE DISPOSITIVE POWER
                                        0
                               -------------------------------------------------
                                  10    SHARED DISPOSITIVE POWER
                                        0
- --------------------------------------------------------------------------------
   11     AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          0
- --------------------------------------------------------------------------------
   12     CHECK BOX IF THE AGGREGATE AMOUNT IN ROW 11 EXCLUDES CERTAIN SHARES*
                                                                       [  ]
- --------------------------------------------------------------------------------
   13     PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)
          0.0%
- --------------------------------------------------------------------------------
   14     TYPE OF REPORTING PERSON*
          IN
- --------------------------------------------------------------------------------
                      *SEE INSTRUCTIONS BEFORE FILLING OUT



                                  SCHEDULE 13D

      Item 1.     Security and Issuer.

            This Statement on Schedule 13D (the "Statement") relates to the
            Common Stock, $.0001 par value per share, (the "Common Stock") of
            Siga Technologies, Inc., a Delaware corporation (the "Issuer"). The
            principal executive offices of the Issuer are located at 420
            Lexington Avenue, Suite 620, New York, New York, 10170.

      Item 2.     Identity and Background.

            (a)   This   statement   is  filed  on  behalf  of  Donald  G.
                  Drapkin,  the Drapkin  Family  Charity  Foundation  (the
                  "Charity"),  Gabriel M. Cerrone,  Panetta  Partners Ltd.
                  ("Panetta"),  Thomas E. Constance and Eric A. Rose, M.D.
                  (collectively,  the "Reporting  Persons").  See attached
                  Exhibit  A  which  is  a  copy  of  their  agreement  in
                  writing  to file  this  statement  jointly  on behalf of
                  each of them.  Each of the  Reporting  Persons has made,
                  and  will   continue   to  make,   its  own   investment
                  decisions  with  respect to  securities  of the  Issuer.
                  Each Reporting  Person  expressly  disclaims  membership
                  in a "group"  with any other  person  within the meaning
                  of Rule  13d-5(b)(1) of the  Securities  Exchange Act of
                  1934, as amended.

            (b)   The  business  address  of each of Mr.  Drapkin  and the
                  Charity  is 35 East 62nd  Street,  New  York,  New York,
                  10021.  The  business  address  of each  of Mr.  Cerrone
                  and  Panetta is 265 East 66th  Street,  Suite  16G,  New
                  York,  New York,  10021.  The  business  address  of Mr.
                  Constance  is 919 Third  Avenue,  41st Floor,  New York,
                  New York,  10022.  The  business  address of Dr. Rose is
                  112 East 78th Street, New York, New York, 10021.

            (c)   Mr.   Drapkin  is  a  Director  and  Vice   Chairman  of
                  MacAndrews   &  Forbes   Holdings   Inc.,   a   Delaware
                  corporation  having its address at 35 East 62nd  Street,
                  New York,  New York,  10021 and is the sole  Trustee  of
                  the  Charity.   The  Charity  is  a  charitable   trust,
                  organized  under  the laws of New  Jersey.  Mr.  Cerrone
                  is an investment  banker,  consultant  and stock broker,
                  and the sole  general  partner  of  Panetta,  a Colorado
                  limited  partnership the principal  business of which is
                  delivering  consulting  services.  Mr.  Constance  is  a
                  Senior  Partner of Kramer Levin  Naftalis & Frankel LLP,
                  a law firm in New York City.  Dr.  Rose is  Chairman  of
                  the  Department of Surgery and  Surgeon-in-Chief  of the
                  Columbia  Presbyterian  Center of New York  Presbyterian
                  Hospital.

            (d)   The Reporting Persons and their respective managing members,
                  officers, directors, general partners, investment managers,
                  and trustees have not, during the five years prior to the date
                  hereof, been convicted in a criminal proceeding (excluding
                  traffic violations or similar misdemeanors).

            (e)   The  Reporting  Persons  and their  respective  managing
                  members,   officers,    directors,   general   partners,
                  investment  managers,  and trustees have not, during the
                  five  years  prior to the date  hereof,  been party to a
                  civil  proceeding of a judicial or  administrative  body
                  of  competent  jurisdiction,  as a result of which  such
                  person  was  or is  subject  to a  judgment,  decree  or
                  final  order   enjoining   future   violations   of,  or
                  prohibiting   or   mandating   activities   subject  to,
                  Federal  or  State   securities   laws  or  finding  any
                  violation with respect to such laws.

            (f)   Mr.  Drapkin,  Mr. Cerrone,  Mr.  Constance and Dr. Rose
                  are citizens of the United States.

      Item 3.     Source and Amount of Funds or Other Consideration

            Pursuant to a Securities Purchase Agreement between Mr. Drapkin and
            the Issuer, dated as of January 31, 2000, (the "Purchase Agreement")
            a copy of which is filed as Exhibit B hereto, Mr. Drapkin purchased
            (i) $500,000 principal amount of 6% Convertible Debentures due
            January 31, 2002 of the Issuer ("Debentures"), a copy of which is
            filed as Exhibit C hereto, with $500,000 of his personal funds, and
            (ii) a warrant (an "Investor Warrant"), a copy of which is filed as
            Exhibit D hereto, to purchase up to 347,826 shares of Common Stock
            at an exercise price of $3.4059 per share, with $17,391.30 of his
            personal funds. The principal amount of, and accrued interest on,
            the Debentures are convertible into Common Stock at the option of
            the holder at any time prior to the maturity date, at a conversion
            price of $1.4375 per share. As of January 31, 2001, the principal
            and accrued interest on Mr. Drapkin's Debentures were convertible
            into an aggregate of 368,696 shares of Common Stock.

                               Page 8 of 13 pages



            Pursuant to a Distributor's Agreement between Fahnestock & Co., Inc.
            and the Issuer, dated as of January 27, 2000, and in connection with
            the Issuer's private placement of Debentures,  Fahnestock designated
            Mr.  Cerrone  to  receive,   and  he  was  issued,  a  warrant  (the
            "Distributor  Warrant"),  a copy of  which is  filed  as  Exhibit  E
            hereto,  to  purchase  up to  210,000  shares of Common  Stock at an
            exercise  price of $1.45 per share.  Mr.  Cerrone then  assigned the
            Distributor Warrant to Panetta.  Pursuant to a Consulting  Agreement
            between  Fahnestock & Co. Inc.  and the Issuer,  dated as of October
            31, 2000,  Fahnestock & Co. Inc., designated Panetta to receive, and
            Panetta  was  issued,  a  warrant  (the  "Consulting  Warrant"  and,
            together with the Investor Warrant and the Distributor  Warrant, the
            "Warrants")  to purchase up to 303,200  shares of Common Stock at an
            exercise  price  of $2.00  per  share,  a copy of which is  attached
            hereto as Exhibit F. The  Consulting  Warrant  was issued to Panetta
            partially  in  consideration  for the  cancellation  of a warrant to
            purchase  303,200  shares of Common  Stock at an  exercise  price of
            $5.00 per share, a copy of which is filed as Exhibit G hereto,  that
            had been issued to Mr. Cerrone in connection with the Issuer's March
            2000 equity  financing.  The Distributor  Warrant and the Consulting
            Warrant  each  contain   provisions   granting  the  holder  certain
            registration rights.

            The Debentures and the Warrants each provides that, with certain
            limited exceptions, they are not convertible or exercisable, as the
            case may be, if, as a result of such action, the number of shares of
            Common Stock beneficially owned by the holder thereof and its
            affiliates (other than shares of Common Stock which may be deemed
            beneficially owned through the ownership of the unexercised portion
            of such securities) would exceed 9.99% of the outstanding shares of
            Common Stock. As a result of the restrictions described in the
            immediately preceding sentence (the "9.99% Limit") and the other
            securities which the Mr. Drapkin may be deemed beneficially to own,
            as of April 6, 2001, Mr. Drapkin's Debentures and Investor Warrant
            are not presently convertible or exercisable. The Issuer may require
            the Investor Warrant to be exercised (subject to the same 9.99%
            Limit) within five days if both (i) the registration statement with
            respect to the shares of Common Stock issuable thereupon is
            effective and (ii) the closing bid price for the Common Stock for
            each of any 15 consecutive trading days is at least 200% of the
            exercise price of the Investor Warrant at such time. Exceptions to
            the 9.99% Limit include the existence of a tender offer for the
            Issuer's common stock.

            Between June 26, 2000 and December 22, 2000, Mr. Drapkin engaged in
            open market transactions through which he acquired a net 373,400
            shares of Common Stock. On November 9, 2000, the Charity purchased
            11,750 shares of Common Stock on the open market. Between February
            9, 2000 and March 13, 2000, Mr. Cerrone purchased 61,500 shares of
            Common Stock on the open market. Mr. Cerrone then assigned such
            shares to Panetta. Mr. Drapkin, the Charity and Mr. Cerrone used
            their respective general funds for such purchases.

            Mr. Drapkin made the following purchases:

               Date              No. of Shares   Purchase Price
               ----              -------------   --------------

               6/26/2000            31,500             $4.037
               6/27/2000             2,000             $3.977
               6/29/2000             5,000             $4.037
               7/6/2000              2,500             $4.54
               7/27/2000             4,000             $4.049
               8/2/2000             20,500             $3.947
               8/3/2000              1,600             $3.906
               8/4/2000              4,000             $3.747
               8/7/2000                500             $3.812
               8/8/2000              2,500             $3.581
               8/10/2000             5,000             $3.532
               8/11/2000             6,000             $4.122
               8/11/2000            50,000             $4.065
               8/14/2000            50,000             $4.399
               8/15/2000             1,100             $3.906
               8/16/2000             2,000             $3.967
               8/24/2000            12,500             $3.30
               8/25/2000            17,500             $3.406
               8/28/2000            11,000             $3.457
               8/29/2000             7,500             $3.195
               8/31/2000            10,000             $3.084

                               Page 9 of 13 pages



               Date              No. of Shares   Purchase Price
               ----              -------------   --------------

               9/14/2000             4,100             $3.004
               9/25/2000            20,500             $3.498
               9/27/2000               100             $2.906
               9/29/2000            40,000             $4.039
               11/3/2000             2,500             $4.175
               11/30/2000           20,500             $4.047
               12/1/2000             4,000             $3.852
               12/5/2000            40,000             $4.508
               12/22/2000           10,000             $3.026


            Mr. Drapkin made the following sale:

               Date              No. of Shares     Sales Price

               9/19/2000            15,000             $3.386


            The Charity made the following purchase:

               Date              No. of Shares   Purchase Price

               11/9/2000            11,750             $4.932


            Mr. Cerrone made the following purchases:

               Date              No. of Shares   Purchase Price
               ----              -------------   --------------

               2/9/2000             16,100             $4.589
               2/10/2000             3,900             $4.551
               2/11/2000            10,500             $4.560
               2/18/2000            12,100             $5.308
               2/22/2000             2,400             $5.369
               2/23/2000            12,500             $5.406
               3/2/2000              2,500             $5.986
               3/13/2000             1,500             $9.158


            In connection with the Management Restructuring Agreement (as
            defined in Item 4, below), each of Judson A. Cooper and Joshua D.
            Schein, Ph.D. agreed to grant an irrevocable proxy (collectively,
            the "Proxies") to Mr. Drapkin on the Effective Date (as defined in
            the Management Restructuring Agreement) giving Mr. Drapkin voting
            power over an aggregate of 905,632 shares of Common Stock owned by
            such parties (the "Proxy Shares") together with any shares of
            capital stock of the Issuer that such parties may acquire subsequent
            to the date of the Proxies (including, without limitation, upon the
            exercise of options held by Mr. Cooper and Mr. Schein, to purchase
            up to an aggregate of 1,400,002 shares of Common Stock).

            Each Reporting Person disclaims beneficial ownership of all the
            Common Stock except Common Stock held by such Reporting Person that
            were purchased on the open market. Each Reporting Person disclaims
            beneficial ownership of the securities held by any other party.

      Item 4.     Purpose of Transaction.

            Each Reporting Person which acquired securities of the Issuer did so
            as an investment in the Issuer. Except as indicated in this Schedule
            13D, no Reporting Person currently has any plans or proposals that
            relate to, or would result in, any of the matters described in
            subparagraphs (a) through (j) of Item 4 of Schedule 13D.

            In connection with the Purchase Agreement, Mr. Drapkin entered into
            a Registration Rights Agreement with the Issuer, dated as of January
            31, 2000, ("Registration Rights Agreement"), a copy of which is
            filed as Exhibit H hereto. Pursuant to the Registration Rights
            Agreement, the Issuer agreed: (i) to file no later than 30 days
            after the Closing Date (as defined in the Purchase Agreement), a
            Registration Statement under

                               Page 10 of 13 pages



             the Securities Act of 1933, as amended, (the "Required Registration
             Statement")  covering  the  resale of the  shares  of Common  Stock
             issuable   upon   conversion  of  principal  and  interest  of  the
             Debentures  and upon  exercise of the Warrant;  and (ii) to use its
             reasonable best efforts to cause such Registration  Statement to be
             declared effective no later than the earlier of (x) five days after
             notice by the  Securities  and Exchange  Commission  that it may be
             declared  effective  and (y) 90 days after the Closing Date. On May
             10, 2000, the Issuer filed the Required Registration Statement and,
             on May 24, 2000,  it was declared  effective.  The shares of Common
             Stock issuable upon exercise of the  Distributor  Warrant were also
             included in the Required Registration Statement.

             Pursuant to a letter agreement, dated as of March 30, 2001, among
             Mr. Drapkin, the Issuer, Mr. Cerrone, Mr. Constance, Dr. Rose,
             Judson A. Cooper and Joshua D. Schein, Ph.D. (the "Management
             Restructuring Agreement"), a copy of which is filed as Exhibit I
             hereto, the Reporting Person has the right to be and to have his
             designees elected to the Board of Directors of the Issuer (the
             "Board") on the Effective Date. The Management Restructuring
             Agreement also provides that the members of the Board at such time
             would be caused to resign from the Board and from any and all
             offices held with the Issuer. Pursuant to the Management
             Restructuring Agreement, Judson A. Cooper and Joshua D. Schein have
             agreed to resign from the Board of the Issuer, and from all other
             offices held with the Issuer, effective as of the Effective Date.
             Mr. Drapkin has designated Mr. Cerrone, Mr. Constance and Dr. Rose
             for election to the Board in accordance with the Management
             Restructuring Agreement. Mr. Drapkin may or may not seek, together
             with the rest of the Board, to fill any vacancies on the Board that
             result from the resignations pursuant to the Management
             Restructuring Agreement.

             Each Reporting Person may from time to time acquire, or dispose of,
             Common Stock and/or other securities of the Issuer if and when it
             deems it appropriate. Each Reporting Person may formulate other
             purposes, plans or proposals relating to any securities of the
             Issuer to the extent deemed advisable in light of market
             conditions, investment policies and other factors.

      Item 5.     Interest in Securities of Issuer.

            (a)   As of April 6,  2001:  Mr.  Drapkin,  as the  holder  of
                  securities  of the  Issuer,  as  proxyholder  under  the
                  Proxies,  and through the holdings of the  Charity,  may
                  be  deemed  beneficially  to  own  1,290,782  shares  of
                  Common Stock or 17.3% of the  outstanding  shares,  and,
                  if not  for  the  9.99%  Limit,  Mr.  Drapkin  could  be
                  deemed to  beneficially  own 1,986,434  shares of Common
                  Stock  or 24.4% of the  outstanding  shares  (excluding,
                  in each case,  any shares  issuable  upon  conversion of
                  amounts  other than  principal of the  Debentures);  Mr.
                  Cerrone,  as the sole  general  partner of Panetta,  may
                  be deemed  beneficially  to own 574,700 shares of Common
                  Stock  or 7.2% of the  outstanding  shares;  and each of
                  the Charity,  Panetta,  Mr.  Constance  and Mr. Rose may
                  be deemed  beneficially  to own the  respective  numbers
                  of shares of Common Stock set forth below:


                  Charity         11,750
                  Panetta        574,700
                  Mr. Constance        0
                  Mr. Rose             0


                  Pursuant to Rule 13d-4 promulgated under the Securities
                  Exchange Act of 1934, as amended, each Reporting Person
                  disclaims beneficial ownership of all the Common Stock except
                  shares of Common Stock, if any, held by such Reporting Person
                  that were purchased on the open market. Pursuant to Rule 13d-4
                  promulgated under the Securities Exchange Act of 1934, as
                  amended, each Reporting Person disclaims beneficial ownership
                  of the securities held by any other person.

            (b)   Mr.  Drapkin  has the sole  power  to vote or to  direct
                  the vote and to  dispose  or to direct  the  disposition
                  of the shares  that he owns.  Mr.  Drapkin  has the sole
                  power  to  vote  or to  direct  the  vote  of the  Proxy
                  Shares.  Mr.  Drapkin  and the  Charity may be deemed to
                  share  the  power to vote or to  direct  the vote and to
                  dispose  or to  direct  the  disposition  of the  shares
                  owned by the  Charity.  Mr.  Cerrone and  Panetta  share
                  the power to vote or to direct  the vote and to  dispose
                  or to direct  the  disposition  of the  shares  owned by
                  Panetta.    Neither   Mr.   Constance   nor   Dr.   Rose
                  beneficially owns any shares of Common Stock.

                               Page 11 of 13 pages



            (c)   Other than certain of the open market purchases of Common
                  Stock reported in Item 3 and entering into the Management
                  Restructuring Agreement (to the extent that may be deemed a
                  transaction in the Common Stock), no Reporting Person has
                  engaged in any transactions in the Common Stock of the Issuer
                  in the past 60 days.

            (d)&(e)     Not applicable.

      Item 6.     Contracts, Arrangements,  Understandings or Relationships With
                  Respect to Securities of the Issuer.

                  Pursuant to the Proxies, Mr. Drapkin was appointed proxyholder
                  with respect to certain securities held by Mr. Cooper and Mr.
                  Schein (see Item 3). A form of the Proxies is attached to the
                  Management Restructuring Agreement that is filed as Exhibit I
                  hereto. The Management Restructuring Agreement includes
                  provisions restricting the abilities of the parties thereto to
                  transfer their respective securities of the Issuer.
                  Additionally, Mr. Drapkin has entered into a Lock-Up Agreement
                  with Vincent Fischetti, a copy of which is filed as Exhibit J
                  hereto, pursuant to which Mr. Fischetti is restricted in
                  transferring his securities of the Issuer without Mr.
                  Drapkin's prior written consent.

                  Except as indicated in this Schedule 13D and the exhibits
                  hereto, there is no contract, arrangement, understanding or
                  relationship between the Reporting Person and any other
                  person, with respect to any securities of the Issuer.


      Item 7.     Material to be Filed as Exhibits.

            Exhibit A:  Agreement of Joint Filing of Schedule 13D, dated as
                        of April 6, 2001.

            Exhibit B:  Securities Purchase Agreement between Mr.
                        Drapkin and the Issuer, dated as of January 31,
                        2000.

            Exhibit C:  6% Convertible Debenture due January 31, 2002 of the
                        Issuer in the principal amount of $500,000 issued to Mr.
                        Drapkin, dated as of January 31, 2000.

            Exhibit D:  Common Stock Purchase Warrant to purchase 347,826
                        shares of Common Stock issued to Mr. Drapkin, dated as
                        of January 31, 2000.

            Exhibit E:  Common Stock Purchase Warrant to purchase 210,000
                        shares of Common Stock issued to Mr. Cerrone, dated as
                        of January 31, 2000.

            Exhibit F:  Common Stock Purchase Warrant to purchase 303,200
                        shares of Common Stock, issued to Panetta, dated as of
                        November 10, 2000.

            Exhibit G:  Cancelled Common Stock Purchase Warrant to purchase
                        303,200 shares of Common Stock, issued to Mr. Cerrone,
                        dated as of May 1, 2000.

            Exhibit H:  Registration Rights Agreement between the Issuer
                        and Mr. Drapkin dated as of January 31, 2000.
            Exhibit I:  letter agreement, dated as of March 30, 2001,
                        among Mr. Drapkin, the Issuer, Mr. Cerrone, Mr.
                        Constance, Dr. Rose, Judson A. Cooper and Joshua
                        D. Schein, Ph.D.

            Exhibit J:  Lock-Up Agreement between Mr. Drapkin and
                        Vincent Fischetti.

                               Page 12 of 13 pages



                                   SIGNATURES

      After reasonable inquiry and to the best knowledge and belief of each of
the undersigned, each of the undersigned certifies that the information set
forth in this statement with respect to such undersigned is true, complete and
correct.



Dated:  April 6, 2001     /s/
                          ------------------------------
        Donald G. Drapkin


        DRAPKIN FAMILY CHARITY FOUNDATION


Dated:  April 6, 2001                     By /s/
                                            --------------------------
                                            Name:
                                            Title:


Dated:  April 6, 2001                        /s/
                                            ---------------------------
                                            Gabriel M. Cerrone


                                            PANETTA PARTNERS LTD.


Dated:  April 6, 2001                       By  /s/
                                              --------------------------
                                              Name:  Gabriel M. Cerrone
                                              Title: General Partner


Dated:  April 6, 2001                           /s/
                                              ---------------------------
                                              Thomas E. Constance


Dated:  April 6, 2001                           /s/
                                              ---------------------------
                                              Eric A. Rose, M.D.


                               Page 13 of 13 pages




                                    EXHIBIT A

                                  AGREEMENT OF

                          JOINT FILING OF SCHEDULE 13D


      The undersigned hereby agree jointly to prepare and file with regulatory
authorities a Schedule 13D and any future amendments thereto reporting each of
the undersigned's ownership of securities of SIGA Technologies, Inc. and hereby
affirm that such Schedule 13D is being filed on behalf of each of the
undersigned.


                                       DRAPKIN FAMILY CHARITY FOUNDATION


Dated:  April 6, 2001                  By  /s/
                                          --------------------------
                                          Name:
                                          Title:


Dated:  April 6, 2001                     /s/
                                          --------------------------
                                          Gabriel M. Cerrone


                                          PANETTA PARTNERS LTD.


Dated:  April 6, 2001                     By /s/
                                            -------------------------
                                            Name:  Gabriel M. Cerrone
                                            Title: General Partner


Dated:  April 6, 2001                       /s/
                                            -------------------------
                                            Thomas E. Constance


Dated:  April 6, 2001                       /s/
                                            -------------------------
                                            Eric A. Rose, M.D.



                                                                       Exhibit B


                          SECURITIES PURCHASE AGREEMENT

            THIS SECURITIES PURCHASE AGREEMENT, dated as of the date of
acceptance set forth below, is entered into by and between SIGA PHARMACEUTICALS,
INC., a Delaware corporation, with headquarters located at 420 Lexington Avenue,
Suite 620, New York, New York 10170 (the "Company"), and each entity named on a
signature page hereto (each, a "Buyer") (each agreement with a Buyer being
deemed a separate and independent agreement between the Company and such Buyer,
except that each Buyer acknowledges and consents to the rights granted to each
other Buyer under such agreement and the Transaction Agreements, as defined
below, referred to therein).

                              W I T N E S S E T H:

            WHEREAS, the Company and the Buyer are executing and delivering this
Agreement in accordance with and in reliance upon the exemption from securities
registration afforded, inter alia, by Rule 506 under Regulation D ("Regulation
D") as promulgated by the United States Securities and Exchange Commission (the
"SEC") under the Securities Act of 1933, as amended (the "1933 Act"), and/or
Section 4(2) of the 1933 Act; and

            WHEREAS, the Buyer wishes to purchase, upon the terms and subject to
the conditions of this Agreement, 6% Convertible Debentures of the Company which
which will be convertible into shares of Common Stock, $.0001 par value per
share, of the Company (the "Common Stock"), upon the terms and subject to the
conditions of such Convertible Debentures, together with the Warrants (as
defined below) exercisable for the purchase of shares of Common Stock (the
"Warrant Shares"), and subject to acceptance of this Agreement by the Company;

            NOW THEREFORE, in consideration of the premises and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties agree as
follows:

            1. AGREEMENT TO PURCHASE; CERTAIN DEFINITIONS.

            a.  Purchase.  The  undersigned  hereby  agrees to purchase from the
Company  6%  Convertible  Debentures  in the  principal  amount set forth on the
signature page of this Agreement (the "Debentures"),  out of a total offering of
$1,500,000 of such Debentures,  and having the terms and conditions and being in
the form attached  hereto as Annex I. The purchase price for the Debentures (the
"Debenture  Purchase  Price") shall be as set forth on the signature page hereto
and shall be payable in United States Dollars.

            b. Certain Definitions.  As used herein, each of the following terms
has the meaning set forth below, unless the context otherwise requires:

            (i) "Closing Date" means the date of the closing of the purchase and
sale of the Debentures, as provided herein.

            (ii)  "Converted  Shares" means the shares of Common Stock  issuable
upon conversion of the Debentures or in lieu of interest payable thereon.



            (iii) "Securities" means the Debentures, the Warrants and the Common
Stock  issuable (x) upon the conversion of the Debentures or in lieu of interest
payable thereon or (y) upon the exercise of the Warrants.

            (iv) "Shares" means the shares of Common Stock  representing  any or
all of the Converted  Shares and other shares to be issued pursuant to the terms
of this Agreement and the Warrant Shares.

            (v) "Warrant  Shares" means the shares of Common Stock issuable upon
exercise of the Warrants.

            (vi) "Purchase Price" means the sum of the Debenture  Purchase Price
and the Warrant Purchase Price (as defined below).

            (vii)  "Effective Date" means the effective date of the Registration
Statement covering the Registrable Securities (as those terms are defined in the
Registration Rights Agreement defined below).

            c. Form of Payment; Delivery of Certificates.

            (i) The Buyer shall pay the Purchase Price by delivering immediately
available  good funds in United States  Dollars to the escrow agent (the "Escrow
Agent") identified in the Joint Escrow Instructions  attached hereto as Annex II
(the "Joint Escrow Instructions") on the date prior to the Closing Date.

            (ii) No later  than the  Closing  Date,  but in any  event  promptly
following  payment by the Buyer to the Escrow Agent of the Purchase  Price,  the
Company  shall  deliver  the  Debentures  and the  Warrants  (collectively,  the
"Certificates"),  each duly  executed on behalf of the Company and issued in the
name of the Buyer, to the Escrow Agent.

            (iii) By signing this Agreement,  each of the Buyer and the Company,
subject  to  acceptance  by the  Escrow  Agent,  agrees  to all of the terms and
conditions of, and becomes a party to, the Joint Escrow Instructions, all of the
provisions of which are incorporated herein by this reference as if set forth in
full.

            d. Method of Payment.  Payment  into  escrow of the  Purchase  Price
shall be made by wire transfer of funds to:

                  Bank of New York
                  350 Fifth Avenue
                  New York, New York 10001

                  ABA# 021000018
                  For credit to the account of Krieger & Prager LLP, Esqs.
                  Account No.:  [To be provided to the Buyer by Krieger &
                                Prager LLP]
                  Re:   Siga Transaction

                                       2



Not later than 5:00 p.m., New York time, on the date which is two (2) New York
Stock Exchange ("NYSE") trading days after the Company shall have accepted this
Agreement and returned a signed counterpart of this Agreement to the Escrow
Agent by facsimile, the Buyer shall deposit with the Escrow Agent the Purchase
Price in currently available funds. Time is of the essence with respect to such
payment, and failure by the Buyer to make such payment, shall allow the Company
to cancel this Agreement.

            e.  Escrow  Property.   The  Purchase  Price  and  the  Certificates
delivered to the Escrow Agent as  contemplated  by Sections  1(c) and (d) hereof
are referred to as the "Escrow Property."

            2. BUYER REPRESENTATIONS,  WARRANTIES,  ETC.; ACCESS TO INFORMATION;
INDEPENDENT INVESTIGATION.

            The Buyer represents and warrants to, and covenants and agrees with,
the Company as follows:

            a. Without  limiting Buyer's right to sell the Common Stock pursuant
to the  Registration  Statement,  the Buyer is purchasing the Debentures and the
Warrants  and will be  acquiring  the Shares for its own account for  investment
only and not with a view towards the public sale or distribution thereof and not
with a view to or for sale in connection with any distribution thereof.

            b. The Buyer is (i) an "accredited investor" as that term is defined
in Rule 501 of the General Rules and Regulations under the 1933 Act by reason of
Rule 501(a)(3),  (ii) experienced in making investments of the kind described in
this Agreement and the related documents,  (iii) able, by reason of the business
and  financial  experience  of its  officers  (if an  entity)  and  professional
advisors (who are not  affiliated  with or compensated in any way by the Company
or any of its  affiliates  or selling  agents),  to protect its own interests in
connection with the  transactions  described in this Agreement,  and the related
documents,  and (iv) able to afford the  entire  loss of its  investment  in the
Securities.

            c. All subsequent  offers and sales of the Debentures and the Shares
by the Buyer shall be made pursuant to registration of the Shares under the 1933
Act or pursuant to an exemption from registration.

            d. The Buyer  understands  that the Securities are being offered and
sold to it in reliance on specific exemptions from the registration requirements
of United  States  federal  and state  securities  laws and that the  Company is
relying  upon the truth and accuracy of, and the Buyer's  compliance  with,  the
representations,  warranties, agreements,  acknowledgments and understandings of
the Buyer  set  forth  herein in order to  determine  the  availability  of such
exemptions and the eligibility of the Buyer to acquire the Securities.

            e. The Buyer and its advisors,  if any, have been furnished with all
materials  relating to the business,  finances and operations of the Company and
materials  relating to the offer and sale of the Debentures and the offer of the
Shares which have been  requested by the Buyer,  including  Annex V hereto.  The
Buyer and its  advisors,  if any,  have been  afforded  the  opportunity  to ask
questions of the Company and have received complete and satisfactory

                                       3



answers to any such inquiries. Without limiting the generality of the foregoing,
the Buyer has also had the opportunity to obtain and to review the Company's (1)
Annual  Report on Form 10-KSB for the fiscal year ended  December 31, 1998,  (2)
Quarterly  Reports on Form 10-Q for the fiscal quarters ending on March 31, 1999
and June 30, 1999 and on Form 10-QSB for the fiscal  quarter  ended on September
30,  1999,  and (3) the Notice  and Proxy  Statement  for the Annual  Meeting of
Shareholders  of the  Company  filed on  January  14,  2000  (collectively,  the
"Company's SEC Documents"). .

            f. The  Buyer  understands  that its  investment  in the  Securities
involves a high degree of risk.

            g. The Buyer  understands  that no United  States  federal  or state
agency or any other government or governmental  agency has passed on or made any
recommendation or endorsement of the Securities.

            h. This Agreement has been duly and validly authorized, executed and
delivered  on behalf of the Buyer and is a valid and  binding  agreement  of the
Buyer enforceable in accordance with its terms,  subject as to enforceability to
general principles of equity and to bankruptcy, insolvency, moratorium and other
similar laws affecting the enforcement of creditors' rights generally.

            3. COMPANY REPRESENTATIONS, ETC. The Company represents and warrants
to the Buyer as of the date  hereof and as of the Closing  Date that,  except as
otherwise provided in Annex V hereto:

            a. Concerning the Debentures.  There are no preemptive rights of any
stockholder of the Company, as such, to acquire the Debentures,  the Warrants or
the Shares.

            b.  Reporting  Company  Status.  The Company is a  corporation  duly
organized,  validly existing and in good standing under the laws of the State of
Delaware and has the  requisite  corporate  power to own its  properties  and to
carry on its business as now being conducted. The Company is duly qualified as a
foreign  corporation to do business and is in good standing in each jurisdiction
where the nature of the business  conducted  or property  owned by it makes such
qualification necessary,  other than those jurisdictions in which the failure to
so qualify would not have a material adverse effect on the business,  operations
or  financial  condition  or  results  of  operation  of  the  Company  and  its
subsidiaries  taken as a whole.  The Company has registered its Common Stock and
is  obligated  to file  reports  pursuant to Section 12 of the 1934 Act, and the
Common Stock is listed and traded on The NASDAQ/SmallCap Market. The Company has
received  no notice,  either  oral or  written,  with  respect to the  continued
eligibility of the Common Stock for such listing, and the Company has maintained
all requirements for the continuation of such listing.

            c. Authorized  Shares.  The authorized  capital stock of the Company
consists of (i) 25,000,000  shares of Common Stock,  $.0001 par value per share,
of which, as of January 27, 2000,  6,602,712  shares are  outstanding,  and (ii)
10,000,000  shares of Preferred  Stock,  $.0001 par share,  none of which, as of
January 27, 2000, none was  outstanding.  All issued and  outstanding  shares of
Common Stock have been duly authorized and validly issued and are

                                       4



fully paid and nonassessable. The Company has sufficient authorized and unissued
shares of Common Stock as may be necessary to effect the issuance of the Shares.
The Shares have been duly  authorized and, when issued upon conversion of, or as
interest on, the Debentures or upon exercise of the Warrants, each in accordance
with its  respective  terms,  will be duly and  validly  issued,  fully paid and
nonassessable  and will not subject the holder thereof to personal  liability by
reason of being such holder.

            d. Securities Purchase Agreement;  Registration Rights Agreement and
Stock. This Agreement and the Registration  Rights Agreement,  the form of which
is attached hereto as Annex IV (the "Registration  Rights  Agreement"),  and the
transactions  contemplated thereby, have been duly and validly authorized by the
Company.  This Agreement has been duly executed and delivered by the Company and
this Agreement is, and each of the other  Transaction  Agreements,  which,  when
executed and delivered by the Company,  will be, valid and binding agreements of
the Company enforceable in accordance with their respective terms, subject as to
enforceability  to general  principles of equity and to bankruptcy,  insolvency,
moratorium,  and other  similar laws  affecting  the  enforcement  of creditors'
rights generally.

            e.  Non-contravention.  The execution and delivery of this Agreement
and the  Registration  Rights  Agreement  by the  Company,  the  issuance of the
Securities,  and the  consummation  by the  Company  of the  other  transactions
contemplated by this Agreement and each of the Transaction Agreements do not and
will not conflict  with or result in a breach by the Company of any of the terms
or   provisions   of,  or  constitute  a  default  under  (i)  the  articles  of
incorporation or by-laws of the Company,  each as currently in effect,  (ii) any
indenture, mortgage, deed of trust, or other material agreement or instrument to
which the Company is a party or by which it or any of its  properties  or assets
are bound, including any listing agreement for the Common Stock except as herein
set forth,  (iii) to its  knowledge,  any  existing  applicable  law,  rule,  or
regulation or any applicable  decree,  judgment,  or order of any court,  United
States  federal  or  state  regulatory  body,  administrative  agency,  or other
governmental body having  jurisdiction over the Company or any of its properties
or assets, or (iv) the Company's listing agreement with The Nasdaq Stock Market,
Inc. relating to its Common Stock, except such conflict, breach or default which
would not have a material adverse effect on the business, operations,  condition
(financial  or  otherwise)  or  results of  operations  of the  Company  and its
subsidiaries,  taken as a whole,  or on the  transactions  contemplated  by this
Agreement or any of the other Transaction Agreements.

            f. Approvals.  No  authorization,  approval or consent of any court,
governmental body,  regulatory agency,  self-regulatory  organization,  or stock
exchange or market or the stockholders of the Company is required to be obtained
by the  Company  for the  issuance  and sale of the  Securities  to the Buyer as
contemplated by this Agreement and the other Transaction Agreements, except such
authorizations, approvals and consents that have been obtained.

            g. SEC Filings.  None of the Company's SEC Documents  contained,  at
the time they were filed,  any untrue statement of a material fact or omitted to
state any material fact  required to be stated  therein or necessary to make the
statements  made  therein in light of the  circumstances  under  which they were
made, not misleading. The Company has, since December 1, 1998, timely filed with
the SEC all forms,  reports  and  exhibits  thereto  required to be filed by

                                       5



the Company  under the  Securities  Exchange Act of 1934,  as amended (the "1934
Act") and the regulations promulgated thereunder,

            h. Absence of Certain  Changes.  Since December 31, 1998,  there has
been no material  adverse  change and no  material  adverse  development  in the
business, properties,  operations, condition (financial or otherwise) or results
of operation  of the Company and its  subsidiaries  taken as a whole,  except as
disclosed in the Company's SEC  Documents.  Since  December 31, 1998,  except as
provided in the  Company's  SEC  Documents,  the Company has not (i) incurred or
become  subject to any  material  liabilities  (absolute or  contingent)  except
liabilities  incurred in the ordinary  course of business  consistent  with past
practices; (ii) discharged or satisfied any material lien or encumbrance or paid
any material  obligation  or  liability  (absolute  or  contingent),  other than
current liabilities paid in the ordinary course of business consistent with past
practices;  (iii) declared or made any payment or  distribution of cash or other
property to  stockholders  with  respect to its capital  stock,  or purchased or
redeemed,  or made any material  agreements to purchase or redeem, any shares of
its capital stock; (iv) sold, assigned or transferred any other tangible assets,
or  canceled  any debts or claims,  except in the  ordinary  course of  business
consistent  with past practices;  (v) suffered any substantial  losses or waived
any rights of material value, whether or not in the ordinary course of business,
or suffered the loss of any material amount of existing business;  (vi) made any
changes in  employee  compensation,  except in the  ordinary  course of business
consistent with past practices;  or (vii) experienced any material problems with
labor or  management  in  connection  with the  terms  and  conditions  of their
employment.

            i. Full  Disclosure.  There is no fact known to the  Company  (other
than general  economic  conditions known to the public generally or as disclosed
in the Company's SEC  Documents)  that has not been  disclosed in writing to the
Buyer that (i) would reasonably be expected to have a material adverse effect on
the  business,  operations,  condition  (financial  or  otherwise) or results of
operations  of the Company and its  subsidiaries,  taken as a whole,  (ii) would
reasonably  be expected to materially  and  adversely  affect the ability of the
Company to perform  its  obligations  pursuant to this  Agreement  or any of the
other agreements  contemplated hereby  (collectively,  including this Agreement,
the  "Transaction  Agreements"),  or  (iii)  would  reasonably  be  expected  to
materially and adversely  affect the value of the rights granted to the Buyer in
the Transaction Agreements.

            j. Absence of  Litigation.  Except as set forth in the Company's SEC
Documents, there is no action, suit, proceeding, inquiry or investigation before
or by any  court,  public  board or body  pending  or, to the  knowledge  of the
Company,  threatened  against or affecting the Company,  wherein an  unfavorable
decision,  ruling or finding  would  reasonably  be  expected to have a material
adverse effect on the business,  operations,  condition (financial or otherwise)
or results of operations of the Company and its subsidiaries,  taken as a whole,
or on the  transactions  contemplated  by any of the  Transaction  Agreements or
which  would  reasonably  be  expected  to  adversely  affect  the  validity  or
enforceability  of, or the  authority  or ability of the  Company to perform its
obligations under, any of the Transaction Agreements.

            k.  Absence of Events of  Default.  The Company is not in default in
the performance or observance of any material obligation, agreement, covenant or
condition contained in any material indenture,  mortgage, deed of trust or other
material  instrument  or

                                       6



agreement to which it is a party or by which it or its property is bound. Except
as set forth in Section  3(e)  hereof,  no Event of Default  (or its  equivalent
term),  as defined in the respective  agreement to which the Company is a party,
and no event  which,  with the giving of notice or the  passage of time or both,
would become an Event of Default (or its equivalent term) (as so defined in such
agreement), has occurred and is continuing,  which would have a material adverse
effect on the  business,  operations,  condition  (financial  or  otherwise)  or
results of operations of the Company and its subsidiaries, taken as a whole.

            l. Prior  Issues.  During the twelve (12) months  preceding the date
hereof, the Company has not issued any convertible securities.

            m.  No  Undisclosed  Liabilities  or  Events.  The  Company  has  no
liabilities  or  obligations  other than those  disclosed in the  Company's  SEC
Documents or those  incurred in the ordinary  course of the  Company's  business
since December 31, 1998, and which  individually or in the aggregate,  do not or
would  reasonably  be  expected  not to have a  material  adverse  effect on the
properties,   business,  operations  (financial  or  otherwise)  or  results  of
operations of the Company and its  subsidiaries,  taken as a whole.  No event or
circumstances  has  occurred  or  exists  with  respect  to the  Company  or its
properties, business, operations, financial condition, or results of operations,
which,  under applicable law, rule or regulation,  requires public disclosure or
announcement  prior to the date  hereof by the Company but which has not been so
publicly  announced  or  disclosed.  There  are  no  proposals  currently  under
consideration or currently anticipated to be under consideration by the Board of
Directors or the  executive  officers of the Company  which  proposal  would (x)
change the certificate of  incorporation or other charter document or by-laws of
the Company,  each as currently in effect, with or without shareholder approval,
which change would reduce or otherwise adversely affect the rights and powers of
the shareholders of the Common Stock or (y) materially or  substantially  change
the  business,  assets or capital of the  Company,  including  its  interests in
subsidiaries.

            n.  No  Integrated  Offering.  Neither  the  Company  nor any of its
affiliates  nor any  person  acting  on its or their  behalf  has,  directly  or
indirectly,  at any time since  January 1, 1999,  made any offer or sales of any
security or solicited any offers to buy any security  under  circumstances  that
would eliminate the availability of the exemption from  registration  under Rule
506 of Regulation D in connection  with the offer and sale of the  Securities as
contemplated hereby.

            o. Dilution.  The number of Shares  issuable upon  conversion of the
Debentures  and the  exercise of the  Warrants  may  increase  substantially  in
certain  circumstances.  The Company's  executive  officers and  directors  have
studied and fully  understand the nature of the Securities being sold hereby and
recognize that they have a potential  dilutive effect. The board of directors of
the  Company  has  concluded,  in its good faith  business  judgment,  that such
issuance  is in the best  interests  of the Company  and its  shareholders.  The
Company  specifically  acknowledges that its obligation to issue the Shares upon
conversion of the  Debentures  and upon exercise of the Warrants is binding upon
the Company and enforceable regardless of the dilution such issuance may have on
the ownership  interests of other  shareholders of the Company,  and the Company
will honor every Notice of Conversion (as  contemplated  by the  Debentures) and
every Notice of Exercise Form (as contemplated by the Warrants)  relating to the
exercise of the

                                       7



Warrants  unless the Company is subject to an injunction  (which  injunction was
not sought by the Company) prohibiting the Company from doing so.

            p. Brokers,  Finders. Except for payment of fees to Fahnestock & Co.
Inc. (the "Placement Agent"), payment of which is the sole responsibility of the
Company,  the Company has taken no action  which would give rise to any claim by
any person for brokerage commission,  finder's fees or similar payments by Buyer
relating to this Agreement or the transactions  contemplated hereby. Buyer shall
have no obligation  with respect to such fees or with respect to any claims made
by or on behalf of other Persons for fees of a type contemplated in this Section
3(p) that may be due in connection with the  transactions  contemplated  hereby.
The Company shall  indemnify and hold  harmless  each of Buyer,  its  employees,
officers, directors, agents, and partners, and their respective affiliates, from
and  against  all  claims,  losses,  damages,  costs  (including  the  costs  of
preparation  and attorney's  fees) and expenses  suffered in respect of any such
claimed or existing fees, as and when incurred.

            4. CERTAIN COVENANTS AND ACKNOWLEDGMENTS.

            a.  Transfer  Restrictions.  The  Buyer  acknowledges  that  (1) the
Debentures  have not been and are not being  registered  under the provisions of
the 1933 Act and, except as provided in the Registration  Rights Agreement,  the
Shares have not been and are not being  registered  under the 1933 Act,  and may
not be  transferred  unless (A)  subsequently  registered  thereunder or (B) the
Buyer shall have  delivered  to the  Company an opinion of  counsel,  reasonably
satisfactory in form, scope and substance to the Company, to the effect that the
Securities to be sold or transferred  may be sold or transferred  pursuant to an
exemption  from  such  registration;  (2)  any  sale of the  Securities  made in
reliance  on Rule  144  promulgated  under  the  1933  Act  may be made  only in
accordance  with  the  terms  of said  Rule  and  further,  if said  Rule is not
applicable,  any  resale of such  Securities  under  circumstances  in which the
seller,  or the  person  through  whom the sale is made,  may be deemed to be an
underwriter,  as that term is used in the 1933 Act, may require  compliance with
some other  exemption under the 1933 Act or the rules and regulations of the SEC
thereunder;  and (3)  neither  the  Company  nor any  other  person is under any
obligation to register the Securities  (other than pursuant to the  Registration
Rights  Agreement) under the 1933 Act or to comply with the terms and conditions
of any exemption thereunder.

            b. Restrictive  Legend.  The Buyer  acknowledges and agrees that the
Debentures  and the Warrants,  and, until such time as the Common Stock has been
registered  under  the  1933  Act as  contemplated  by the  Registration  Rights
Agreement  and sold in  accordance  with an  effective  Registration  Statement,
certificates and other instruments representing any of the Securities shall bear
a restrictive  legend in  substantially  the following form (and a stop-transfer
order may be placed against transfer of any such Securities):

            THESE SECURITIES (THE "SECURITIES") HAVE NOT BEEN REGISTERED UNDER
            THE SECURITIES ACT OF 1933, AS AMENDED OR THE SECURITIES LAWS OF ANY
            STATE AND MAY NOT BE SOLD OR OFFERED FOR SALE IN THE ABSENCE OF AN
            EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES OR AN OPINION OF

                                       8




            COUNSEL OR OTHER EVIDENCE ACCEPTABLE TO THE COMPANY THAT SUCH
            REGISTRATION IS NOT REQUIRED.

            c. Filings.  The Company undertakes and agrees to make all necessary
filings  in  connection  with  the sale of the  Securities  to the  Buyer  under
applicable  provisions  of the  1933  Act,  the  1934  Act and  the  regulations
promulgated  thereunder,  or required  by any  domestic  securities  exchange or
trading  market,  and to provide a copy thereof to the Buyer promptly after such
filing.

            d.  Reporting  Status.  So long as the Buyer  beneficially  owns any
Securities, (i) the Company shall file all reports required to be filed with the
SEC pursuant to Section 13 or 15(d) of the 1934 Act and shall not  terminate its
status as an issuer required to file reports under the 1934 Act even if the 1934
Act or the rules and regulations  thereunder  would permit such  termination and
(ii) the Company will take all reasonable action under its control to obtain and
to continue  the listing and  trading of its Common  Stock  (including,  without
limitation,  all Registrable  Securities) on The Nasdaq SmallCap Market and will
comply in all material respects with the Company's  reporting,  filing and other
obligations under the by-laws or rules of the National Association of Securities
Dealers,  Inc.  ("NASD") or The Nasdaq Stock  Market,  Inc. So long as the Buyer
beneficially owns any of the Securities, if the Common Stock ceases to be listed
and traded on an exchange,  or if the Company  terminates it status as an issuer
required  to file  reports  pursuant  to Section 13 or 15(d) of the 1934 Act, it
will take all  reasonable  action  under its  control  to ensure  that  adequate
current  public  information  with  respect  to  the  Company,  as  required  in
accordance with Rule 144(c)(2) of the 1933 Act, is publicly available.

            e.  Use of  Proceeds.  The  Company  currently  intends  to use  the
proceeds from the sale of the Debentures  (excluding amounts paid by the Company
for legal  fees,  finder's  fees,  escrow  fees and other  transaction  expenses
relating to the sale of the Debentures),  for internal working capital purposes,
and, unless specifically  consented to in advance in each instance by the Buyer,
the Company shall not, directly or indirectly, use such proceeds for any loan to
or investment in any other corporation,  partnership  enterprise or other person
or for the repayment of any outstanding loan by the Company to any other party.

            f. Certain Agreements.

            (i) Except to the extent  specifically  provided below,  but in each
such  event  subject  to  compliance  with all of the other  provisions  of this
Agreement,  the Company covenants and agrees that it will not, without the prior
written consent of the Buyer, enter into any subsequent or further offer or sale
of Common Stock or securities convertible into Common Stock (collectively,  "New
Common  Stock")  with any third  party  pursuant to a  transaction  which in any
manner permits the  registration of the Common Stock,  included in or underlying
the new Common  Stock to become  effective  on any date  which is  earlier  than
ninety (90) days after the Effective Date.

            (ii) The  foregoing  provisions  shall not restrict the Company from
(A) issuing  shares of Common  Stock upon the  exercise of certain  warrants and
options for the purchase of shares outstanding as of the date hereof or pursuant
to the  Company's  existing  stock  option

                                       9



plans,  all as scheduled on Annex V hereto,  or (B) issuing or  registering  (or
both) up to 125,000  shares of Common Stock which may have been issued or may be
issuable to Open-i Media, Inc.  ("Open-i")  pursuant to an existing  contractual
obligation of the Company to Open-i. The transactions referred to in clauses (A)
and (B) of this subparagraph (ii) are referred to as "Allowable Transactions."

            (iii) The  provisions of the  subparagraph  (i) of this  Section4(f)
will no longer  apply once one or more of the  Buyers  have,  in the  aggregate,
disposed of seventy-five percent (75%) or more of the Registrable Securities.

            (iv) By the Closing  Date,  the Company  shall obtain the  agreement
(each, a  "Principal's  Agreement") of each of its Principals (as defined below)
that,  without the prior  written  consent of the Buyer in each  instance,  such
Principal  will not sell or  otherwise  transfer  or offer to sell or  otherwise
transfer any shares of Common Stock  (other than shares  originally  acquired by
such Principal in open market transactions)  directly or indirectly held by such
Principal  during  the  period  commencing  on the  date of this  Agreement  and
continuing  through and  including  the date which is ninety (90) days after the
Effective  Date.  Each such  Principal's  Agreement shall (w) specify that it is
entered into as an inducement to the Buyer's execution, delivery and performance
of this Agreement,  (x) name the Buyer as a third party beneficiary thereof, (y)
acknowledge that the Company's transfer agent will be provided with instructions
that transfers by a Principal  require the consent of the Company and the Buyer,
and (z) contemplate  that, in addition to any other damages or remedies that may
be  appropriate,  the  Principal's  Agreement shall be enforceable by injunction
sought by the Company and the Buyer or any one or more of them. A "Principal" is
a person who meets any one or more of the following criteria: (A) each of Joshua
Schein, Judson Cooper, Richard Stone and Vincent Fischetti,  respectively (each,
a "Company  Principal"),  (B) a spouse of a Company  Principal  (a  "Principal's
Spouse") who,  directly or  indirectly,  holds any shares of Common Stock of the
Company,  (C) a parent,  sibling or child of a Company  Principal who resides in
the  household  of a Company  Principal  or of a  Principal's  Spouse  (each,  a
"Principal's  Relative") and who,  directly or  indirectly,  holds any shares of
Common Stock, or (D) any other person or entity, including,  without limitation,
for profit or non-profit  corporations,  partnerships  and trusts,  whose voting
rights  regarding  Common  Stock of the  Company is  subject  to the  direction,
control or other  influence of any Company  Principal,  Principal's  Spouse,  or
Principal's Relative.

            (v) In the event the Company breaches the provisions of this Section
4(f), the Conversion  Price (as defined in the Debenture) shall be amended to be
equal to (x) 90% of (y) the amount  determined in accordance with the provisions
of the  Debentures  without  regard to this  provision,  and the  Purchaser  may
require  the  Company  to  immediately  redeem  all  outstanding  Debentures  in
accordance with Section 4(i)(y) hereof.

            g. Available Shares.  The Company shall have at all times authorized
and reserved for issuance,  free from preemptive rights,  shares of Common Stock
sufficient  to yield the number of shares of Common  Stock as may be required to
satisfy  (i) the  conversion  rights  of all  Buyers  pursuant  to the terms and
conditions of any outstanding Debentures or represent payment of any accrued but
unpaid or future interest on the Debentures,  assuming in each instance that the
Conversion Price was the Minimum Conversion Price (as defined in the Debentures)
and (ii) the exercise rights of all unexercised portions of the Warrants.

                                       10



            h. Warrants. The Company agrees to issue to the Buyer on the Closing
Date  transferable,  divisible  warrants  (the  "Warrants")  for the purchase of
69,565 shares of Common Stock for each $100,000 of the Debenture  Purchase Price
paid by the Buyer.  In  consideration  of the  issuance of the  Warrants,  Buyer
agrees to pay the Company,  at the same time and in same manner as the Debenture
Purchase Price is paid, an amount (the "Warrant  Purchase  Price") equal to $.05
per share covered by such Warrant.  The Warrant  Purchase  Price will be applied
against the amount payable by the Buyer on exercise of the Warrant. The Warrants
shall bear an exercise  price equal to  one-hundred  five percent  (105%) of the
average closing bid price of the Common Stock, as reported by Bloomberg,  LP or,
if not so reported, as reported on the over-the-counter  market, for a period of
five consecutive  trading days ending on the trading day immediately  before the
Closing Date.  The Warrants will expire on the last day of the calendar month in
which the fifth anniversary of the Closing Date occurs. The Warrants shall be in
the form annexed hereto as Annex VI,  together with (x)  registration  rights as
provided in the Registration  Rights  Agreement and (y) piggy-back  registration
rights  after  the  effectiveness  of the  Registration  Statement  expires,  as
contemplated by the Registration Rights Agreement.

            i.  Limitation on Issuance of Shares.  If applicable to the Company,
the Company may be limited in the number of shares of Common  Stock it may issue
by virtue of (i) the number of authorized  shares or (ii) the  applicable  rules
and  regulations  of the markets on which the Common  Stock is listed or traded,
including, but not necessarily limited to, NASDAQ Rule 4310(c)(25)(H)(i) or Rule
4460(i)(1), as may be applicable (collectively, the "Cap Regulations").  Without
limiting the other provisions thereof, the Debentures shall provide that (i) the
Company will take all steps reasonably necessary, including calling a special or
annual  shareholders'  meeting,  to be in a position  to issue  shares of Common
Stock on conversion of the Debentures  without violating the Cap Regulations and
(ii) if, despite taking such steps,  the Company still can not issue such shares
of Common Stock without violating the Cap Regulations, the holder of a Debenture
which cannot be converted as result of the Cap Regulations (each such Debenture,
an "Unconverted Debenture") shall have the option,  exercisable in such holder's
sole and absolute discretion, to elect either of the following remedies:

                  (x) if permitted by the Cap Regulations, require the Company
            to issue shares of Common Stock in accordance with such holder's
            notice of conversion at a conversion purchase price equal to the
            average of the closing price per share of Common Stock for any five
            (5) consecutive trading days (subject to certain equitable
            adjustments for certain events occurring during such period) during
            the sixty (60) trading days immediately preceding the date of notice
            of conversion; or

                  (y) require the Company to redeem each Unconverted Debenture
            for an amount (the "Redemption Amount"), payable in cash, equal to:

                             V            x           M
                        -----------
                            CP

                                       11



            where:

                  "V" means the principal of an  Unconverted  Debenture plus any
            accrued but unpaid interest thereon;

                  "CP" means the conversion price in effect on the date of
            redemption (the "Redemption Date") specified in the notice from the
            holder of the Unconverted Debentures electing this remedy; and

                  "M" means the highest closing ask price per share of the
            Common Stock during the period beginning on the Redemption Date and
            ending on the date of payment of the Redemption Amount.

A holder of an Unconverted Debenture may elect one of the above remedies with
respect to some of such holder's Unconverted Debenture and the other remedy with
respect to other portions of the Unconverted Debenture. The Debentures shall not
contain any provisions inconsistent with the above terms. The provisions of this
paragraph are not intended to limit the scope of the provisions otherwise
included in the Debentures.

            j. Reset Shares.

            (i) If at any time  after  the  Closing  Date and prior to or on the
ninetieth  (90th  day)  after the  Effective  Date,  except  with  respect to an
Allowable Transaction, the Company shall sell or enter into an agreement to sell
Common Stock or securities convertible into Common Stock (a "Reset Transaction")
where the New Yield (as  defined  below)  is  greater  than the then  applicable
Current Yield (as defined  below),  the Company shall issue (x) shares of Common
Stock (the "Reset  Debenture  Shares") to each Buyer (I) on the closing  date of
the Reset  Transaction  (the "Reset  Transaction  Date") in connection with each
conversion  of Debentures  effected  prior to the Reset  Transaction  Date as to
which the Buyer has not yet disposed of the Converted Shares issued to the Buyer
thereby (each, a "Prior  Conversion")  and (II) at the same time as the issuance
of any shares of Common Stock with respect to each subsequent  conversion (each,
a "Subsequent  Conversion")  and (y) warrants to purchase shares of Common Stock
("Reset Warrants") to each Buyer on the Reset Transaction Date (I) in connection
with each exercise of Warrants  effected prior to the Reset  Transaction Date as
to which the Buyer has not yet  disposed  of the  Warrant  Shares  issued to the
Buyer  thereby  (each,  a  "Prior  Exercise")  and (II) in  connection  with the
unexercised  portion of the Warrants held by such Buyer on the Reset Transaction
Date.  The Reset  Debenture  Shares  and the Reset  Warrants  shall be issued in
addition to, and not in lieu of, shares of Common Stock issuable upon conversion
of the Debentures by the Buyer and the Warrants being issued to the Buyer on the
Closing Date.

            (ii) For purposes of this Section 4(j),  the  following  terms shall
have the meanings indicated:

                 (A)  "Principal  Converted"  means  (x) with  respect  to Prior
Conversions,  the  aggregate  principal  amount  of  the  Debentures  previously
converted by the Buyer into Common Stock and (y) with respect to each Subsequent
Conversion,  the principal  amount of the Debentures then being converted by the
Buyer into Common Stock.

                                       12



                 (B)  "Current  Discount"  means the  percentage  determined  by
dividing the Conversion Price by the Current Market Price (as defined below), in
all  events  expressed  as a  decimal,  or, if there has been a  previous  Reset
Transaction  for which Reset  Shares were issued to the Buyer,  the New Discount
applicable to that Reset Transaction, in all events expressed as a decimal.

                 (C) "Current  Yield" means the result of one (1) divided by the
Current Discount.

                 (D) "New  Discount"  means (x) the lowest stated  percentage of
the relevant  market price at which a buyer in the New  Transaction  may convert
the securities  purchased in the Reset Transaction into Common Stock (e.g., 75%)
or if the conversion  price or rate is stated as a percentage  discount from the
relevant  market price,  the result of 1 minus such stated  percentage  discount
(e.g., a "25%  discount" is equal to 75%),  or, (y) if the Reset  Transaction is
for the sale of Common Stock at a fixed  purchase  price per share of the Common
Stock which is less than the New Market Price (as defined below), the percentage
determined  by dividing  such fixed price by the New Market Price (e.g.,  if the
fixed  price  per share of Common  Stock is $4 and the New  Market  Price is $5,
80%), in all events expressed as a decimal.

                 (E) "New Yield"  means the result of one (1) divided by the New
Discount.

                 (F) "Current  Market Price" means the average closing bid price
of the Common Stock as reported by  Bloomberg,  LP for the five (5) trading days
ending on the trading day immediately preceding the Closing Date.

                 (G) "New Market  Price" means the average  closing bid price of
the Common Stock as reported by Bloomberg,  LP or the average  closing bid price
on the  over-the-counter  market,  for the five (5)  trading  days ending on the
trading day  immediately  preceding (i) the date on which the binding  agreement
for the Reset Transaction was entered into,  provided such date is not more than
forty-five  (45) calendar days prior to the Reset  Transaction  Date, or (ii) if
clause (i) does not apply, the Reset Transaction Date.

                 (H)  "Relevant  Market  Price"  means (x) with  respect  to the
computation  of Reset  Debenture  Shares for Prior  Conversions,  the New Market
Price and (y) with respect to the computation of Reset Debenture Shares for each
Subsequent  Conversion,  the average  closing  bid price of the Common  Stock as
reported  by   Bloomberg,   LP  or  the   average   closing  bid  price  on  the
over-the-counter  market for the five (5) trading days ending on the trading day
immediately preceding the relevant effective conversion date.

                 (I)  "Exercisable  Warrants"  means (x) with  respect  to Prior
Exercises,  the aggregate  number of shares as to which the Buyer  exercised the
Buyer's Warrants, plus (y) the aggregate number of shares then remaining subject
to exercise of the Buyer's Warrant.

                 (J) "Debenture Percentage" means the fraction, of which (i) the
numerator is the Principal  Converted and (ii) the  denominator is the Principal
Amount  of the  Debentures  specified  on the  Buyer's  signature  page  to this
Agreement.

                                       13



                 (K) "Disposed Shares  Percentage" means the fraction,  of which
(i) the numerator is the Converted Shares and Warrant Shares  previously sold or
otherwise  disposed  of by the Buyer  and (ii) the  denominator  is the  139,130
shares for each $100,000 of Debenture  Purchase  Price  specified on the Buyer's
signature page to this  Agreement.  At the written request of the Company (which
shall be made to the Placement  Agent,  but not more frequently than once in any
calendar week with respect to each Buyer), the Buyer or the Placement Agent will
confirm  in  writing  that the  Buyer  has not  sold or  otherwise  disposed  of
Converted  Shares and  Warrant  Shares  previously  issued to the Buyer.  If the
Company  does receive such  confirmation  within three (3) business  days of the
Placement Agent's receipt of such request, the Company shall be entitled to deem
that the Buyer has  previously  sold or  otherwise  disposed  of such  Converted
Shares or Warrant Shares.  For purposes of this paragraph (K),  Converted Shares
shall not include shares issued in payment of interest on the Debentures.

                 (L) "Reset  Shares"  means the Reset  Debenture  Shares and the
shares of Common Stock issuable on exercise of Reset Warrants.

            (iii) The  number of Reset  Debenture  Shares  shall be equal to the
result of multiplying the Debenture Percentage by the following fraction:

               (Principal Converted) x (New Yield - Current Yield)
               ---------------------------------------------------
                              Relevant Market Price

            (iv) The  number of Reset  Warrants  shall be equal to the result of
the following calculation:

            (Exercisable Warrants) x ([New Yield - Current Yield]-1)

The Reset Warrants shall have the same terms as the Warrants, including but not
limited to, exercise price for the shares covered by such Reset Warrants.

            (v) With respect to each Buyer individually,  the obligations of the
Company  under this Section  4(j) will cease to apply if such  Buyer's  Disposed
Shares Percentage is seventy-five percent (75%) or more.

            (vi) The  provisions of Section 5(c),  (d) and (e) of this Agreement
shall apply to the Reset Shares.

            5. TRANSFER AGENT INSTRUCTIONS.

            a.  Promptly  following  the  delivery by the Buyer of the  Purchase
Price in  accordance  with  Section 1(c)  hereof,  the Company will  irrevocably
instruct  its  transfer  agent to issue  Common  Stock  from  time to time  upon
conversion of the  Debentures in such amounts as specified  from time to time by
the Company to the transfer agent,  bearing the restrictive  legend specified in
Section 4(b) of this  Agreement  prior to  registration  of the Shares under the
1933  Act,  registered  in the  name of the  Buyer  or its  nominee  and in such
denominations to be specified by the Buyer in connection with each conversion of
the Debentures.  The Company warrants that no instruction  inconsistent with the
instructions referred to in this Section 5 and the stop transfer instructions to
give effect to Section 4(a) hereof prior to registration  and sale of the Shares
under

                                       14



the 1933 Act will be given by the Company to the transfer  agent with respect to
the Shares and that the Shares  shall  otherwise be freely  transferable  on the
books  and  records  of  the  Company  as and to the  extent  provided  in  this
Agreement,  the Registration  Rights  Agreement,  and applicable law. Nothing in
this Section  shall affect in any way the Buyer's  obligations  and agreement to
comply with all applicable securities laws upon resale of the Securities. If the
Buyer provides the Company with an opinion of counsel reasonably satisfactory to
the Company that  registration of a resale by the Buyer of any of the Securities
in  accordance  with  clause  (1)(B) of Section  4(a) of this  Agreement  is not
required under the 1933 Act, the Company shall (except as provided in clause (2)
of Section 4(a) of this Agreement) permit the transfer of the Securities and, in
the case of the  Converted  Shares or the  Warrant  Shares,  as the case may be,
promptly instruct the Company's transfer agent to issue one or more certificates
for  Common  Stock  without  legend  in such name and in such  denominations  as
specified by the Buyer.

            b. (i) The Company  will  permit the Buyer to exercise  its right to
convert the  Debentures by  telecopying  or delivering an executed and completed
Notice of Conversion to the Company and, upon full  conversion of the Debenture,
delivering,  within five (5) business days after the relevant  Conversion  Date,
the original  Debentures are being converted to the Company by express  courier,
with a copy to the transfer agent.

            (ii)  The  term  "Conversion   Date"  means,  with  respect  to  any
conversion  elected by the holder of the  Debentures,  the date specified in the
Notice  of  Conversion,  provided  the  copy  of the  Notice  of  Conversion  is
telecopied  to or  otherwise  delivered  to the Company in  accordance  with the
provisions  hereof so that it is  received  by the  Company  on or  before  such
specified date.

            (iii) The Company will  instruct its transfer  agent to transmit the
certificates  representing  the Converted Shares issuable upon conversion of any
Debentures  to the Buyer at the address  specified  in the Notice of  Conversion
(which may be the  Buyer's  address for  notices as  contemplated  by Section 11
hereof or a different address) via recognized  express or overnight courier,  by
electronic  transfer or  otherwise,  within three (3) business  days (such third
business  day, the  "Instruction  Date") after (A) the business day on which the
Company has received the Notice of Conversion  (by facsimile or other  delivery)
and the original  Debentures  being converted (and if the same are not delivered
to the Company on the same date,  the date of delivery of the last of such items
to be delivered) or (B) the date an interest payment on the Debentures which the
Company has elected to pay by the issuance of Common Stock,  as  contemplated by
the Debentures, was due. In any event, the Company will cause to be delivered to
the Buyer the  certificates  representing  Converted  Shares  (together,  unless
otherwise instructed by the Buyer, with one or more instruments representing the
Debentures  not being so converted if the  instruments  submitted in  connection
with such conversion  represent more principal than then being converted) within
ten (10)  calendar  days (such tenth day,  the  "Delivery  Date")  after (A) the
business  day on which the Company has  received  the Notice of  Conversion  (by
facsimile or other delivery) and the original Debentures being converted (and if
the same are not delivered to the Company on the same date, the date of delivery
of the last of such items to be delivered)  or (B) the date an interest  payment
on the Debentures which the Company has elected to pay by the issuance of Common
Stock, as contemplated by the Debentures, was due.

                                       15



            c. The Company  understands that a delay in instructing its transfer
agent to issue  the  Shares of  Common  Stock  beyond  the  Instruction  Date or
issuance of the shares after the Delivery  Date could result in economic loss to
the Buyer. As compensation to the Buyer for such loss, the Company agrees to pay
payments  to the  Buyer  for late  delivery  of  instructions  to the  Company's
transfer  agent or late issuance of the shares in accordance  with the following
schedule  (where "No.  Business  Days Late" is defined as the number of business
days beyond two (2) business days from the I nstruction  Date or Delivery  Date,
as the case may be.):

                              Late Payment For Each $10,000
                              of Debenture Principal or Interest
No. Business Days Late        Amount Being Converted
- ----------------------        ----------------------
        1                        $100
        2                        $200
        3                        $300
        4                        $400
        5                        $500
        6                        $600
        7                        $700
        8                        $800
        9                        $900
       10                        $1,000
      >10                        $1,000 +$200 for each Business
                                 Day Late in excess of 10 days

The Company shall pay any payments incurred under this Section in immediately
available funds upon demand. Nothing herein shall limit the Buyer's right to
pursue actual damages for the Company's failure to properly instruct its
transfer agent to issue and deliver the Common Stock to the Buyer or to timely
issue the Common Stock to the Buyer. Furthermore, in addition to any other
remedies which may be available to the Buyer, in the event that the Company
fails for any reason to instruct its transfer agent to effect delivery of such
shares of Common Stock within two (2) business days after the Instruction Date
or by the Delivery Date, the Buyer will be entitled to revoke the relevant
Notice of Conversion by delivering a notice to such effect to the Company
whereupon the Company and the Buyer shall each be restored to their respective
positions immediately prior to delivery of such Notice of Conversion.

            d. If, by the  Delivery  Date,  the Company  fails for any reason to
deliver the Shares to be issued upon  conversion of a Debenture  and  thereafter
the holder of the Debentures being converted (a "Converting  Holder") purchases,
in an arm's-length open market transaction or otherwise,  shares of Common Stock
(the "Covering  Shares") in order to make delivery in  satisfaction of a sale of
Common Stock by the Converting  Holder (the "Sold Shares"),  which delivery such
Converting  Holder  anticipated  to make using the Shares to be issued upon such
conversion (a "Buy-In"),  the Converting  Holder shall have the right to require
the  Company  pay to the  Converting  Holder  the Buy-In  Adjustment  Amount (as
defined below) in addition to all other amounts contemplated in other provisions
of the Transaction Agreements,  and not in lieu of any such amounts. The "Buy-In
Adjustment  Amount"  is the  amount  equal  to the  excess,  if any,  of (x) the
Converting Holder's total purchase price (including  brokerage  commissions,  if

                                       16



any)  for  the  Covering  Shares  over  (y) the net  proceeds  (after  brokerage
commissions, if any) received by the Converting Holder from the sale of the Sold
Shares.  The Company  shall pay the Buy-In  Adjustment  Amount to the Company in
immediately available funds immediately upon demand by the Converting Holder. By
way of  illustration  and not in limitation of the foregoing,  if the Converting
Holder purchases shares of Common Stock having a total purchase price (including
brokerage  commissions)  of $11,000 to cover a Buy-In with  respect to shares of
Common Stock it sold for net proceeds of $10,000,  the Buy-In  Adjustment Amount
which Company will be required to pay to the Converting Holder will be $1,000.

            e. In lieu of  delivering  physical  certificates  representing  the
Common Stock issuable upon conversion,  provided the Company's transfer agent is
participating in the Depository Trust Company ("DTC") Fast Automated  Securities
Transfer  program,  upon  request  of the  Buyer  and its  compliance  with  the
provisions contained in this paragraph,  so long as the certificates therefor do
not  bear a legend  and the  Buyer  thereof  is not  obligated  to  return  such
certificate  for the  placement of a legend  thereon,  the Company shall use its
best efforts to cause its transfer agent to  electronically  transmit the Common
Stock issuable upon  conversion to the Buyer by crediting the account of Buyer's
Prime Broker with DTC through its Deposit Withdrawal Agent Commission system.

            f. If, at any time (i) the  Company  challenges,  disputes or denies
the right of a holder of a Debenture  to effect a  conversion  of the  Debenture
into  Common  Stock or  otherwise  dishonors  or rejects any  Conversion  Notice
delivered in accordance  with the terms of this Agreement or the  Certificate of
Designations  or any  exercise  of any  Warrant  in  accordance  with its  terms
("Warrant  Exercise"),  or (ii) any third party who is not and has never been an
Affiliate  of such holder  commences  any  lawsuit or  proceeding  or  otherwise
asserts any claim before any court or public or  governmental  authority,  which
lawsuit,  proceeding or claim seeks to challenge,  deny, enjoin,  limit, modify,
delay or  dispute  the  right of such  holder to effect  the  conversion  of the
Debenture,  into Common  Stock,  which  lawsuit,  proceeding or assertion is not
withdrawn or dismissed within three (3) business days after it was instituted or
made,  and the Company  refuses to honor any such  Conversion  Notice or Warrant
Exercise,  then such  holder  shall  have the right,  by  written  notice to the
Company,  to require the Company to promptly redeem the Debentures for cash at a
redemption  price (the  "Mandatory  Purchase  Amount")  equal to (x) one hundred
thirty  percent  (130%)  of  the  unliquidated   principal  of  the  unconverted
Debentures held by such holder plus (y) all accrued but unpaid  dividends on the
Debentures through the date of payment of the Mandatory Purchase Amount. Nothing
contained  in this Section 5 shall be construed to require the Company to pay to
the Buyer any of the amounts contemplated by this Section 5 for late delivery of
any  certificates or refusal to honor a Notice of Conversion or Warrant Exercise
to the extent  that such delay or refusal is caused by the Buyer (but  exclusion
of the delay or refusal of the  Company  shall be limited  only to the period of
such delay or refusal which was directly caused by an uncured action or omission
of the Buyer and not to periods beyond the cure of such action or omission by or
on behalf of the Buyer).  Under any of the  circumstances  set forth above,  the
Company shall be  responsible  for the payment of all costs and expenses of such
holder,  including,  but not necessarily  limited to,  reasonable legal fees and
expenses,  as and when incurred in connection  with such holder's  disputing any
such action or pursuing such holder's rights hereunder (in addition to any other
rights such holder may have hereunder or otherwise).

                                       17



            g. The holder of any  Debentures  shall be entitled to exercise  its
conversion  privilege  with  respect  to  the  Debentures   notwithstanding  the
commencement of any case under 11 U.S.C.ss. 101 et seq. (the "Bankruptcy Code").
In the event the  Company is a debtor  under the  Bankruptcy  Code,  the Company
hereby waives, to the fullest extent permitted, any rights to relief it may have
under 11  U.S.C.ss.362  in respect of such holder's  conversion  privilege.  The
Company hereby waives, to the fullest extent permitted,  any rights to relief it
may have under 11  U.S.C.ss.362  in respect of the conversion of the Debentures.
The  Company  agrees,  without  cost or  expense to such  holder,  to take or to
consent  to  any  and  all  action  necessary  to  effectuate  relief  under  11
U.S.C.ss.362.

            h. The Company will authorize its transfer agent to give information
relating  to the Company  directly  to the Buyer or the Buyer's  representatives
upon the  request of the Buyer or any such  representative  , to the extent such
information  relates  to (i) the  status of shares  of  Common  Stock  issued or
claimed to be issued to the Buyer in connection with a Notice of Conversion,  or
(ii) the number of outstanding  shares of Common Stock of all stockholders as of
a current or other  specified  date.  The Company  will provide the Buyer with a
copy of the authorization so given to the transfer agent.

            6. CLOSING DATE.

            a. The  Closing  Date  shall  occur on the date  which is the  first
trading  day on  The  Nasdaq  SmallCap  Market  after  each  of  the  conditions
contemplated by Sections 7 and 8 hereof shall have either been satisfied or been
waived by the party in whose favor such conditions run.

            b. The closing shall occur on the Closing Date at the offices of the
Escrow  Agent and shall take place no later  than 3:00 P.M.,  New York time,  on
such day or such other time as is  mutually  agreed  upon by the Company and the
Buyer.

            c.  Notwithstanding  anything to the contrary  contained herein, the
Escrow Agent will be  authorized  to release the Escrow Funds to the Company and
to others and to release the other  Escrow  Property  on the  Closing  Date upon
satisfaction  of the  conditions  set forth in  Sections  7 and 8 hereof  and as
provided in the Joint Escrow Instructions.

            7. CONDITIONS TO THE COMPANY'S OBLIGATION TO SELL.

The Buyer understands that the Company's obligation to sell the Debentures and
the Warrants to the Buyer pursuant to this Agreement on the Closing Date is
conditioned upon:

            a. The execution and delivery of this Agreement and the Registration
Rights Agreement by the Buyer;

            b.  Delivery  by the  Buyer to the  Escrow  Agent  of good  funds as
payment in full of an amount equal to the Purchase Price in accordance with this
Agreement;

            c. The  accuracy  on the  Closing  Date of the  representations  and
warranties  of the Buyer  contained in this  Agreement,  each as if made on such
date,  and the  performance by the

                                       18



Buyer on or  before  such  date of all  covenants  and  agreements  of the Buyer
required to be performed on or before such date; and

            d.  There  shall  not be in  effect  any  law,  rule  or  regulation
prohibiting or restricting the transactions  contemplated  hereby,  or requiring
any consent or approval which shall not have been obtained.

            8. CONDITIONS TO THE BUYER'S OBLIGATION TO PURCHASE.

            The Company understands that the Buyer's obligation to purchase the
Debentures and the Warrants pursuant to this Agreement on the Closing Date is
conditioned upon:

            a. The execution and delivery of this Agreement and the Registration
Rights Agreement by the Company;

            b.  Delivery by the Company to the Escrow Agent of the  Certificates
in accordance with this Agreement;

            c. The accuracy in all material  respects on the Closing Date of the
representations and warranties of the Company contained in this Agreement.  each
as if made on such date,  and the  performance  by the Company on or before such
date of all covenants and agreements of the Company  required to be performed on
or before such date;

            d. On the Closing Date,  the Buyer shall have received an opinion of
counsel for the Company,  dated such Closing Date, in form,  scope and substance
reasonably  satisfactory to the Buyer,  substantially to the effect set forth in
Annex III attached hereto;

            e.  There  shall  not be in  effect  any  law,  rule  or  regulation
prohibiting or restricting the transactions  contemplated  hereby,  or requiring
any consent or approval which shall not have been obtained;

            f. From and after the date hereof to and including the Closing Date,
the trading of the Common Stock shall not have been  suspended by the SEC or the
NASD and  trading in  securities  generally  on the NYSE or The  NASDAQ/SmallCap
Market shall not have been  suspended or limited,  nor shall minimum prices been
established for securities traded on The NASDAQ/SmallCap Market, nor shall there
be any outbreak or escalation of hostilities  involving the United States or any
material  adverse  change in any  financial  market  that in either  case in the
reasonable  judgment  of the Buyer  makes it  impracticable  or  inadvisable  to
purchase the Debentures.

            9. GOVERNING LAW: MISCELLANEOUS.

            a. This Agreement shall be governed by and interpreted in accordance
with the laws of the State of New York for  contracts to be wholly  performed in
such state and without  giving effect to the  principles  thereof  regarding the
conflict  of laws.  Each of the  parties  consents  to the  jurisdiction  of the
federal courts whose districts encompass any part of the City of New York or the
state  courts  of the  State  of New  York  sitting  in the  City of New York in
connection with any dispute  arising under this Agreement and hereby waives,  to
the maximum  extent

                                       19



permitted by law, any  objection,  including  any  objection  based on forum non
conveniens, to the bringing of any such proceeding in such jurisdictions. To the
extent  determined by such court,  the Company shall reimburse the Buyer for any
reasonable legal fees and disbursements  incurred by the Buyer in enforcement of
or protection of any of its rights under any of the Transaction Agreements.

            b.  Failure of any party to exercise  any right or remedy under this
Agreement or otherwise,  or delay by a party in exercising such right or remedy,
shall not operate as a waiver thereof.

            c. This Agreement  shall inure to the benefit of and be binding upon
the successors and assigns of each of the parties hereto.

            d. All pronouns and any  variations  thereof refer to the masculine,
feminine or neuter, singular or plural, as the context may require.

            e. A facsimile  transmission of this signed Agreement shall be legal
and binding on all parties hereto.

            f. This Agreement may be signed in one or more counterparts, each of
which shall be deemed an original.

            g. The headings of this  Agreement are for  convenience of reference
and shall not form part of, or affect the interpretation of, this Agreement.

            h.  If  any  provision  of  this  Agreement   shall  be  invalid  or
unenforceable in any jurisdiction, such invalidity or unenforceability shall not
affect the validity or  enforceability of the remainder of this Agreement or the
validity or enforceability of this Agreement in any other jurisdiction.

            i. This  Agreement  may be amended only by an  instrument in writing
signed by the party to be charged with enforcement thereof.

            j. This Agreement supersedes all prior agreements and understandings
among the parties hereto with respect to the subject matter hereof.

            10.  NOTICES.  Any notice  required or permitted  hereunder shall be
given in  writing  (unless  otherwise  specified  herein)  and  shall be  deemed
effectively given on the earliest of

                  (a)      the date delivered, if delivered by personal delivery
                           as against written  receipt  therefor or by confirmed
                           facsimile transmission,

                  (b)      the  seventh  business  day  after  deposit,  postage
                           prepaid,  in the  United  States  Postal  Service  by
                           registered or certified mail, or

                  (c)      the third  business  day  after  mailing  by  express
                           courier, with delivery costs and fees prepaid,

                                       20



in each case, addressed to each of the other parties thereunto entitled at the
following addresses (or at such other addresses as such party may designate by
ten (10) days' advance written notice similarly given to each of the other
parties hereto):

COMPANY:                Siga Pharmaceuticals, Inc.
                        At its address at the head of this Agreement
                        Attn: Judson Cooper
                        Telephone No.: (212) 672-9150
                        Telecopier No.: (212) 697-3130

                        and with a copy to:

                        Orrick Herrington & Sutcliffe, LLP
                        666 Fifth Avenue
                        New York, NY 10103
                        Attn: Jeffrey Fessler, Esq.
                        Telephone No.: (212) 506-5000
                        Telecopier No.: (212) 506-5151

BUYER:                  At the address set forth on the signature page of this
                        Agreement.

                        with a copy to:

                        Krieger & Prager, Esqs.
                        319 Fifth Avenue
                        Attn: Samuel Krieger, Esq.
                        New York, New York 10016
                        Telephone No.: (212) 689-3322
                        Telecopier No. (212) 213-2077

ESCROW AGENT:           Krieger & Prager, Esqs.
                        319 Fifth Avenue
                        Attn: Samuel Krieger, Esq.
                        New York, New York 10016
                        Telephone No.: (212) 689-3322
                        Telecopier No.: (212) 213-2077

            11. SURVIVAL OF  REPRESENTATIONS  AND WARRANTIES.  The Company's and
the Buyer's  representations  and warranties  herein shall survive the execution
and  delivery of this  Agreement  and the delivery of the  Certificates  and the
Warrants and the payment of the Purchase  Price,  and shall inure to the benefit
of the Buyer and the Company and their respective successors and assigns.

                                       21



            IN WITNESS WHEREOF, this Agreement has been duly executed by the
Buyer by one of its officers thereunto duly authorized as of the date set forth
below.

PRINCIPAL AMOUNT OF DEBENTURES:               $500,000
                                               -------
DEBENTURE PURCHASE PRICE:                                       $500,000
                                                                 -------
NUMBER OF WARRANTS(1):                         347,826
                                               -------
WARRANT PURCHASE PRICE(2):                                      $ 17,391.30
                                                                 ----------
TOTAL PURCHASE PRICE:                                           $517,391.30
                                                                 ----------

                            SIGNATURES FOR INDIVIDUAL

            IN WITNESS WHEREOF, the undersigned represents that the foregoing
statements are true and correct and that it has caused this Securities Purchase
Agreement to be duly executed on its behalf this 26 day of January, 2000.

c/o 35 East 62 Street                     Donald G. Drapkin
- ------------------------------------      -------------------------------------
Address                                   Printed Name of Subscriber
New York, NY    10021
                                          By:  /s/ Donald G. Drapkin
                                               --------------------------------
                                          (Signature of Authorized Person)
Telecopier No. 212/572-5184
               ---------------------
Resident:   P.O. Box 1040                 _____________________________________
            Rio Vista Drive               Printed Name and Title
____________Alpine NJ  07620____
Jurisdiction of Incorporation
or organization


As of the date set forth below, the undersigned hereby accepts this Agreement
and represents that the foregoing statements are true and correct and that it
has caused this Securities Purchase Agreement to be duly executed on its behalf.

SIGA PHARMACEUTICALS, INC

By:    /s/ Judson Cooper
       ------------------------------
Title: Chairman
       ------------------------------
Date: January 31, 2000
      -------------------------------


- -----------------
(1) 69,565 per $100,000 Debenture Purchase Price.

(2) $0.05 per share covered by the Warrant.


                                       22




                                                                       Exhibit C


      NEITHER THESE SECURITIES NOR THE SECURITIES ISSUABLE UPON CONVERSION
      HEREOF HAVE BEEN REGISTERED WITH THE UNITED STATES SECURITIES AND EXCHANGE
      COMMISSION OR THE SECURITIES COMMISSION OF ANY STATE OR UNDER THE
      SECURITIES ACT OF 1933 (THE "1933 ACT"), AS AMENDED. THE SECURITIES ARE
      RESTRICTED AND MAY NOT BE OFFERED, RESOLD, PLEDGED OR TRANSFERRED EXCEPT
      AS PERMITTED UNDER THE 1933 ACT PURSUANT TO REGISTRATION OR EXEMPTION OR
      SAFE HARBOR THEREFROM.

No. 00A-1                                                       US $500,000.00

                           SIGA PHARMACEUTICALS, INC.

                6% CONVERTIBLE DEBENTURE DUE JANUARY 31, 2002

      THIS DEBENTURE is one of a duly authorized issue of up to $1,500,000 in
Debentures of SIGA PHARMACEUTICALS, INC., a corporation organized and existing
under the laws of the State of Delaware (the "Company") designated as its 6%
Convertible Debentures. Such Debentures may be issued in series, each of which
may have a different maturity date, but which otherwise have substantially
similar terms. Capitalized terms not defined herein shall have the meanings
ascribed to them in the Securities Purchase Agreement, dated January 31, 2000,
by and among the Company and the Buyers (as that term is defined therein) (the
"Securities Purchase Agreement").

      FOR VALUE RECEIVED, the Company promises to pay to DONALD G. DRAPKIN, the
registered holder hereof (the "Holder"), the principal sum of Five Hundred
Thousand and 00/100 Dollars (US $500,000.00) on January 31, 2002 (the "Maturity
Date") and to pay interest on the principal sum outstanding from time to time in
arrears (i) upon conversion as provided herein, (ii) upon redemption as provided
herein or (iii) on the Maturity Date, at the rate of 6% per annum accruing from
January 31, 2000, the date of initial issuance of this Debenture. Accrual of
interest shall commence on the first such business day to occur after the date
hereof and shall continue to accrue on a daily basis until payment in full of
the principal sum has been made or duly provided for.

      This Debenture is subject to the following additional provisions:

      1. The Debentures are issuable in denominations of Ten Thousand and 00/100
Dollars (US  $10,000.00)  and integral  multiples  thereof.  The  Debentures are
exchangeable for an equal aggregate  principal amount of Debentures of different
authorized  denominations,  as requested by the Holder surrendering the same. No
service charge will be made for such registration or transfer or exchange.



      2. The  Company  shall be  entitled  to  withhold  from  all  payments  of
principal  of, and  interest  on,  this  Debenture  any  amounts  required to be
withheld under the applicable provisions of the United States income tax laws or
other applicable laws at the time of such payments, and Holder shall execute and
deliver all required documentation in connection therewith.

      3. This Debenture has been issued subject to investment representations of
the  original  purchaser  hereof and may be  transferred  or  exchanged  only in
compliance  with the  Securities  Act of 1933, as amended (the "1933 Act"),  and
other  applicable  state  and  foreign  securities  laws  and the  terms  of the
Transaction Agreements. In the event of any proposed transfer of this Debenture,
the Company may  require,  prior to issuance of a new  Debenture  in the name of
such other person, that it receive reasonable transfer  documentation  including
legal  opinions  that the issuance of the  Debenture in such other name does not
and will not  cause a  violation  of the  1933  Act or any  applicable  state or
foreign  securities  laws.  Prior  to  due  presentment  for  transfer  of  this
Debenture,  the  Company  and any agent of the  Company  may treat the person in
whose name this Debenture is duly registered on the Company's Debenture Register
as the owner hereof for the purpose of receiving  payment as herein provided and
for all other  purposes,  whether or not this Debenture is overdue,  and neither
the Company nor any such agent shall be affected by notice to the contrary.

      4. (A) The Holder of this Debenture is entitled, at its option, subject to
the following  provisions of this Section 4, to convert all or a portion of this
Debenture into shares of Common Stock of the Company, $.0001 par value per share
("Common Stock") of the Company at any time (except as set forth in this Section
4(A) or in Section 4(C)  hereunder)  prior to the Maturity Date, at a conversion
price (the "Conversion  Price") for each share of Common Stock equal to $1.4375,
as such amount may be equitably adjusted in accordance with Sections 8, 9 and 10
hereof,  if applicable.  The minimum principal amount a Buyer may convert is the
lower of (x) at least US  $10,000  (unless  if at the time of such  election  to
convert the  aggregate  principal  amount of all  Debentures  registered  to the
Holder  is less  than US  $10,000,  then the whole  amount  thereof)  or (y) the
maximum  amount  which the  Holder  can then  convert  pursuant  to the terms of
Section 4(C) hereof.

         (B)  Conversion  shall be effectuated by delivery by facsimile or other
delivery  to the Company of the form of  conversion  notice  attached  hereto as
Exhibit A  executed  by the Holder of the  Debenture  evidencing  such  Holder's
intention to convert this Debenture or a specified  portion  hereof  ("Notice of
Conversion"),  and accompanied, if required by the Company, by proper assignment
hereof in blank.  Subject to the  provisions  of Section 4(C)  hereof,  interest
accrued or accruing from the date of issuance to the date of  conversion  shall,
at the option of the Company, be paid in cash or Common Stock upon conversion at
the Conversion  Price  applicable to such  conversion.  No fractional  shares of
Common  Stock or scrip  representing  fractions  of  shares  will be  issued  on
conversion,  but the number of shares  issuable  shall be rounded to the nearest
whole share.  The date on which notice of conversion is given shall be deemed to
be the date on which  the  Holder  faxes or  otherwise  delivers  the  Notice of
Conversion, duly executed, to the Company (the "Conversion Date"), provided that
the Holder shall deliver to the Company the original  Debentures being converted
within five (5) business days  thereafter.  Facsimile  delivery of the Notice of
Conversion  shall be accepted by the Company at facsimile number (212) 697-3130;
ATTN: President.  Certificates representing Common Stock upon

                                      -2-



conversion  will be  delivered  within  three (3) business  days  following  the
Conversion  Date,  except  as  otherwise  provided  in the  Securities  Purchase
Agreement.

         (C)  Notwithstanding  any other provision hereof, of the Warrants or of
any of the other Transaction Agreements, in no event (except (i) with respect to
an automatic or mandatory conversion,  if any, of a Debenture as provided in the
Debentures,  (ii) as specifically  provided in this Debenture as an exception to
this  provision,  or (iii) while there is  outstanding a tender offer for any or
all of the shares of the Company's Common Stock) shall the Holder be entitled to
convert any Debenture or shall the Company have the  obligation,  to convert all
or any portion of this  Debenture  (and the Company  shall not have the right to
pay interest on this  Debenture in the form of Common Stock) to the extent that,
after  such  conversion,  the sum of (1) the  number of  shares of Common  Stock
beneficially owned by the Holder and its affiliates (other than shares of Common
Stock  which may be deemed  beneficially  owned  through  the  ownership  of the
unconverted  portion of the Debentures or unexercised  portion of the Warrants),
and (2) the number of shares of Common Stock issuable upon the conversion of the
Debentures or exercise of the Warrants  with respect to which the  determination
of this  proviso is being made,  would  result in  beneficial  ownership  by the
Holder and its affiliates of more than 9.99% of the outstanding shares of Common
Stock (after taking into account the shares to be issued to the Holder upon such
conversion  or  exercise).  For  purposes  of the  proviso  to  the  immediately
preceding sentence,  beneficial ownership shall be determined in accordance with
Section  13(d) of the  Securities  Exchange  Act of 1934,  as amended (the "1934
Act"), except as otherwise provided in clause (1) of such sentence.  The Holder,
by its acceptance of this Debenture, further agrees that if the Holder transfers
or assigns any of the Debentures to a party who or which would not be considered
such an affiliate,  such assignment shall be made subject to the transferee's or
assignee's specific agreement to be bound by the provisions of this Section 4(C)
as if such transferee or assignee were the original Holder hereof.

         (D) The Holder recognizes that the Company may be limited in the number
of shares of Common Stock it may issue by (i) reason of its  authorized  shares,
or (ii) the applicable rules and regulations of the principal  securities market
on  which  the  Common  Stock  is  listed  or  traded  (collectively,  the  "Cap
Regulations").  Without  limiting the other provisions  hereof,  (i) the Company
will take all steps reasonably  necessary to be in a position to issue shares of
Common  Stock  on  conversion  of  the  Debentures  without  violating  the  Cap
Regulations  and (ii) if,  despite  taking such steps,  the Company still cannot
issue such shares of Common Stock  without  violating the Cap  Regulations,  the
Holder  of this  Debenture  (to the  extent  the  same can not be  converted  in
compliance with the Cap Regulations (an  "Unconverted  Debenture")),  shall have
the option,  exercisable in the Holder's sole and absolute discretion,  to elect
any one of the following remedies:

                  (x) if permitted by the Cap Regulations, require the Company
            to issue shares of Common Stock in accordance with such Holder's
            Notice of Conversion relating to the Unconverted Debenture at a
            conversion purchase price equal to the average of the closing bid
            price per share of Common Stock for any five (5) consecutive trading
            days (subject to the equitable adjustments for certain events

                                      -3-



            occurring during such period as provided in this Debenture) during
            the sixty (60) trading days immediately preceding the date of the
            Notice of Conversion; or

                  (y) require the Company to redeem each Unconverted Debenture
            for an amount (the "Cap Redemption Amount"), payable in cash, equal
            to:

                             V            x           M
                        -----------
                            CP

                  where:

                  "V" means the outstanding principal plus accrued interest
            through the Cap Redemption Date (as defined below) of an Unconverted
            Debenture;

                  "CP" means the Conversion Price in effect on the date of
            redemption (the "Cap Redemption Date") specified in the notice from
            the Holder electing this remedy; and

                  "M" means the highest closing ask price per share during the
            period beginning on the Cap Redemption Date and ending on the date
            of payment of the Cap Redemption Amount.

The holder of an Unconverted Debenture may elect one of the above remedies with
respect to a portion of such Unconverted Debenture and the other remedy with
respect to other portions of the Unconverted Debenture.

         (E) Anything herein to the contrary  notwithstanding,  in the event the
Company  breaches  the  provisions  of Section 4(f) of the  Securities  Purchase
Agreement,  the  Conversion  Price  shall be  amended  to be equal to 90% of the
Conversion  Price  determined in accordance with Section 4(A) of this Debenture,
and the Holder may  require the Company to  immediately  redeem the  outstanding
portion of this Debenture in accordance with clause (y) of Section 4(D).


5.     [Intentionally omitted]


      6. Subject to the terms of the Securities Purchase Agreement, no provision
of this Debenture shall alter or impair the obligation of the Company,  which is
absolute  and  unconditional,  to pay the  principal  of, and  interest on, this
Debenture at the time,  place,  and rate,  and in the coin or  currency,  herein
prescribed in accordance with its terms. This Debenture and all other Debentures
now or hereafter issued of similar terms are direct obligations of the Company.

      7. No recourse  shall be had for the payment of the  principal  of, or the
interest  on, this  Debenture,  or for any claim based  hereon,  or otherwise in
respect hereof, against any incorporator,  shareholder,  officer or director, as
such,  past,  present or future,  of the Company or

                                      -4-



any successor  corporation,  whether by virtue of any  constitution,  statute or
rule of law, or by the  enforcement  of any  assessment or penalty or otherwise,
all  such  liability  being,  by  the  acceptance  hereof  and  as  part  of the
consideration for the issue hereof, expressly waived and released.

      8. If the Company merges or consolidates with another corporation or sells
or transfers all or  substantially  all of its assets to another  person and the
holders  of the  Common  Stock are  entitled  to receive  stock,  securities  or
property in respect of or in exchange for Common  Stock,  then as a condition of
such  merger,  consolidation,  sale  or  transfer,  the  Company  and  any  such
successor,  purchaser or transferee  agree that the Debenture may  thereafter be
converted  on the terms and subject to the  conditions  set forth above into the
kind and amount of stock,  securities or property  receivable  upon such merger,
consolidation,  sale or  transfer  by a holder of the number of shares of Common
Stock into which this  Debenture  might have been converted  immediately  before
such merger, consolidation, sale or transfer, subject to adjustments which shall
be as nearly  equivalent  as may be  practicable.  In the event of any  proposed
merger,  consolidation  or sale or transfer of all or  substantially  all of the
assets of the  Company (a  "Sale"),  the Holder  hereof  shall have the right to
convert this  Debenture  by  delivering  a Notice of  Conversion  to the Company
within fifteen (15) days of receipt of notice of such Sale from the Company.

      9. If, for any reason, prior to the conversion or redemption,  the Company
spins off or otherwise divests itself of a part of its business or operations or
disposes all of or a substantial  part of its assets in a transaction (the "Spin
Off") in which the Company  does not  receive  compensation  for such  business,
operations or assets,  but causes  securities  of another  entity (the "Spin Off
Securities") to be issued to security  holders of the Company,  then the Company
shall cause (i) to be reserved Spin Off  Securities  equal to the number thereof
which  would have been issued to the Holder had all of the  Holder's  Debentures
outstanding  on the record date (the "Record Date") for  determining  the amount
and  number  of Spin Off  Securities  to be issued to  security  holders  of the
Company  (the  "Outstanding  Debentures")  been  converted  as of the  close  of
business on the trading day  immediately  before the Record Date (the  "Reserved
Spin Off Shares"),  and (ii) to be issued to the Holder on the conversion of all
or any of the  Outstanding  Debentures,  such  amount of the  Reserved  Spin Off
Shares equal to (x) the Reserved  Spin Off Shares  multiplied by (y) a fraction,
of which (I) the numerator is the principal amount of the Outstanding Debentures
then being  converted,  and (II) the denominator is the principal  amount of the
Outstanding Debentures.

      10.  If,  at  any  time  while  any  portion  of  this  Debenture  remains
outstanding, the Company effectuates a stock split or reverse stock split of its
Common  Stock or issues a dividend on its Common Stock  consisting  of shares of
Common Stock, the Conversion  Price shall be equitably  adjusted to reflect such
action. By way of illustration,  and not in limitation, of the foregoing: (i) if
the  Company  effectuates  a 2:1 split of its  Common  Stock,  thereafter,  with
respect to any  conversion  for which the  Company  issues the shares  after the
record date of such split,  the Conversion  Price shall be deemed to be one-half
of the Conversion Price in effect  immediately  prior to such split; (ii) if the
Company effectuates a 1:10 reverse split of its Common Stock,  thereafter,  with
respect to any  conversion  for which the  Company  issues the shares  after the
record date of such reverse split,  the  Conversion  Price shall be deemed to be
ten times the Conversion  Price in effect  immediately  prior to such split; and
(iii) if the Company  declares a stock dividend of one share of Common Stock for
every 10 shares  outstanding,  thereafter,  with respect to any  conversion  for
which the Company issues the

                                      -5-



shares after the record date of such  dividend,  the  Conversion  Price shall be
deemed to be the amount of the Conversion Price in effect  immediately  prior to
such record date multiplied by a fraction,  of which the numerator is the number
of shares (10) for which a dividend share will be issued and the  denominator is
such  number of shares plus the  dividend  share(s)  issuable or issued  thereon
(11).

      11. All payments contemplated hereby to be made "in cash" shall be made in
immediately  available  good funds in such coin or currency of the United States
of America as at the time of payment is legal  tender for  payment of public and
private debts.  All payments of cash and each delivery of shares of Common Stock
issuable to the Holder as contemplated hereby shall be made to the Holder at the
address last appearing on the Debenture Register of the Company as designated in
writing by the Holder from time to time;  except that the Holder can  designate,
by notice to the  Company,  a  different  delivery  address  for any one or more
specific payments or deliveries.

      12. The Holder of the Debenture,  by acceptance  hereof,  agrees that this
Debenture is being  acquired for  investment  purposes and that such Holder will
not offer,  sell or otherwise  dispose of this Debenture or the Shares of Common
Stock issuable upon conversion thereof except under circumstances which will not
result in a  violation  of the Act or any  applicable  state Blue Sky or foreign
laws or similar laws relating to the sale of securities.

      13. This Debenture  shall be governed by and construed in accordance  with
the  laws  of the  State  of  Delaware.  Each  of the  parties  consents  to the
jurisdiction  of the federal  courts whose  districts  encompass any part of the
City of Wilmington  or the state courts of the State of Delaware  sitting in the
City of Wilmington in connection  with any dispute  arising under this Agreement
and hereby  waives,  to the maximum  extent  permitted  by law,  any  objection,
including any  objection  based on forum non  coveniens,  to the bringing of any
such proceeding in such  jurisdictions.  To the extent determined by such court,
the  Company  shall  reimburse  the  Holder  for any  reasonable  legal fees and
disbursements  incurred by the Holder in  enforcement of or protection of any of
its rights under any of this Debenture.

      14. The following shall constitute an "Event of Default":

                  a.       The Company shall default in the payment of principal
                           or interest on this Debenture and same shall continue
                           for a period of ten (10) days; or

                  b.       Any of the  representations or warranties made by the
                           Company herein, in the Securities Purchase Agreement,
                           the   Registration

                                      -6-



                           Rights  Agreement or in any  certificate or financial
                           or other written  statements  heretofore or hereafter
                           furnished  by the  Company  in  connection  with  the
                           execution  and  delivery  of  this  Debenture  or the
                           Securities  Purchase  Agreement  shall  be  false  or
                           misleading in any material  respect at the time made;
                           or

                  c.       The Company  fails to issue shares of Common Stock to
                           the  Holder or to cause its  Transfer  Agent to issue
                           shares of Common Stock upon exercise by the Holder of
                           the  conversion  rights of the  Holder in  accordance
                           with the terms of this  Debenture,  fails to transfer
                           or to  cause  its  Transfer  Agent  to  transfer  any
                           certificate  for shares of Common Stock issued to the
                           Holder upon  conversion  of this  Debenture  and when
                           required by this Debenture or the Registration Rights
                           Agreement,  and such transfer is otherwise lawful, or
                           fails to remove  any  restrictive  legend or to cause
                           its Transfer Agent to transfer on any  certificate or
                           any shares of Common  Stock issued to the Holder upon
                           conversion of this  Debenture as and when required by
                           this  Debenture,  the  Agreement or the  Registration
                           Rights Agreement and such legend removal is otherwise
                           lawful,  and any such failure shall continue  uncured
                           for five (5) business days after written  notice from
                           the Holder of such failure; or

                  d.       The Company shall fail to perform or observe,  in any
                           material   respect,   any   other   covenant,   term,
                           provision,  condition, agreement or obligation of any
                           Debenture  in this  series  and  such  failure  shall
                           continue  uncured  for a period of  thirty  (30) days
                           after written notice from the Holder of such failure;
                           or

                  e.       The Company shall fail to perform or observe,  in any
                           material  respect,  any  covenant,  term,  provision,
                           condition,  agreement  or  obligation  of the Company
                           under  the  Securities   Purchase  Agreement  or  the
                           Registration  Rights Agreement and such failure shall
                           continue  uncured  for a period of  thirty  (30) days
                           after written  notice from the Holder of such failure
                           (other  than a  failure  to  cause  the  Registration
                           Statement  to  become  effective  no  later  than the
                           Required  Effective  Date, as defined and provided in
                           the  Registration  Rights  Agreement,  as to which no
                           such cure period shall apply); or

                  f.       The Company  shall (1) admit in writing its inability
                           to pay its debts  generally as they mature;  (2) make
                           an  assignment   for  the  benefit  of  creditors  or
                           commence  proceedings  for  its  dissolution;  or (3)
                           apply for or consent to the appointment of a trustee,
                           liquidator  or receiver for its or for a  substantial
                           part of its property or business; or

                  g.       A trustee,  liquidator or receiver shall be appointed
                           for  the  Company  or for a  substantial  part of its
                           property  or  business

                                      -7-



                           without  its  consent  and  shall  not be  discharged
                           within sixty (60) days after such appointment; or

                  h.       Any  governmental  agency or any  court of  competent
                           jurisdiction  at the  instance  of  any  governmental
                           agency shall  assume  custody or control of the whole
                           or  any  substantial  portion  of the  properties  or
                           assets of the  Company  and  shall  not be  dismissed
                           within sixty (60) days thereafter; or

                  i.       Any money judgment, writ or warrant of attachment, or
                           similar  process  in excess of Two  Hundred  Thousand
                           ($200,000)  Dollars in the aggregate shall be entered
                           or filed against the Company or any of its properties
                           or other assets and shall remain  unpaid,  unvacated,
                           unbonded or unstayed  for a period of sixty (60) days
                           or in any event later than five (5) days prior to the
                           date of any proposed sale thereunder; or

                  j.       Bankruptcy, reorganization, insolvency or liquidation
                           proceedings or other proceedings for relief under any
                           bankruptcy  law or any law for the  relief of debtors
                           shall be instituted by or against the Company and, if
                           instituted   against  the   Company,   shall  not  be
                           dismissed or stayed within sixty (60) days after such
                           institution  or the  Company  shall by any  action or
                           answer  approve of,  consent to, or  acquiesce in any
                           such  proceedings  or admit the material  allegations
                           of, or default in  answering a petition  filed in any
                           such proceeding; or

                  k.       The Company shall have its Common Stock  suspended or
                           delisted from an exchange or over-the-counter  market
                           from trading for in excess of five (5) trading  days;
                           or

                  l.       The Company fails to file the Registration  Statement
                           within sixty (60) days  following the Closing Date or
                           the Registration  Statement is not declared effective
                           within one  hundred  fifty (150) days  following  the
                           Closing Date.

Then, or at any time thereafter, and in each and every such case, unless such
Event of Default shall have been waived in writing by the Holder (which waiver
shall not be deemed to be a waiver of any subsequent default) at the option of
the Holder and in the Holder's sole discretion, the Holder may consider this
Debenture immediately due and payable, without presentment, demand, protest or
notice of any kinds, all of which are hereby expressly waived, anything herein
or in any note or other instruments contained to the contrary notwithstanding,
and the Holder may immediately enforce any and all of the Holder's rights and
remedies provided herein or any other rights or remedies afforded by law.


                                      -8-



      15. Nothing  contained in this Debenture  shall be construed as conferring
upon the  Holder  the right to vote or to  receive  dividends  or to  consent or
receive notice as a shareholder in respect of any meeting of shareholders or any
rights  whatsoever  as a  shareholder  of the Company,  unless and to the extent
converted in accordance with the terms hereof.

      16. In the event for any  reason,  any payment by or act of the Company or
the Holder  shall  result in payment of interest  which  would  exceed the limit
authorized  by or be in violation of the law of the  jurisdiction  applicable to
this  Debenture,  the  obligation of the Company to pay interest or perform such
act or requirement  shall be reduced to the limit  authorized under such law, so
that in no event  shall  the  Company  be  obligated  to pay any such  interest,
perform any such act or be bound by any  requirement  which would  result in the
payment  of  interest  in excess of the  limit so  authorized.  In the event any
payment by or act of the Company  shall  result in the  extraction  of a rate of
interest in excess of a sum which is lawfully collectible as interest, then such
amount (to the extent of such excess not returned to the Company) shall, without
further  agreement or notice between or by the Company or the Holder,  be deemed
applied to the payment of principal,  if any, hereunder immediately upon receipt
of such excess funds by the Holder, with the same force and effect as though the
Company had specifically  designated such sums to be so applied to principal and
the Holder had agreed to accept such sums as an interest-free prepayment of this
Debenture.  If any part of such excess remains after the principal has been paid
in full, whether by the provisions of the preceding sentences of this Section 16
or otherwise,  such excess shall be deemed to be an interest-free  loan from the
Company to the Holder,  which loan shall be payable  immediately  upon demand by
the  Company.  The  provisions  of this  Section 16 shall  control  every  other
provision of this Debenture.

      IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed by an officer thereunto duly authorized.

Dated: _________________, 2000

                                    SIGA PHARMACEUTICALS, INC.


                                    By:  /s/ Judson Cooper
                                         -------------------------

                                    Judson Cooper
                                    ------------------------------
                                    (Print Name)
                                    Chairman
                                    ------------------------------
                                    (Title)


                                      -9-



                                    EXHIBIT A

                              NOTICE OF CONVERSION

 (To be Executed by the Registered Holder in order to Convert the Debenture)


The undersigned hereby irrevocably elects to convert  $________________ of the
principal  amount of the above Debenture No. __ into Shares of Common Stock of
Siga  Pharmaceuticals,  Inc.  (the  "Company")  according  to  the  conditions
hereof, as of the date written below.

Conversion Date*

__________________________________________


Applicable Conversion Price

__________________________________________


Signature

__________________________________________
          [Name]

Address:

__________________________________________

__________________________________________



- -------------------
* This original Debenture must be received by the Company by the fifth business
date following the Conversion Date.



                                      -10-




                                                                       Exhibit D


      THESE SECURITIES INCLUDING ANY UNDERLYING SECURITIES (THE "SECURITIES")
      HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
      THE SECURITIES LAWS OF ANY STATE AND MAY NOT BE SOLD OR OFFERED FOR SALE
      IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES
      OR AN OPINION OF COUNSEL OR OTHER EVIDENCE ACCEPTABLE TO THE COMPANY THAT
      SUCH REGISTRATION IS NOT REQUIRED.

                           SIGA PHARMACEUTICALS, INC.

                          COMMON STOCK PURCHASE WARRANT

         1. Issuance; Certain Definitions. In consideration of good and valuable
consideration,   the   receipt   of  which  is  hereby   acknowledged   by  SIGA
PHARMACEUTICALS, INC., a Delaware corporation (the "Company"), DONALD G. DRAPKIN
or registered  assigns (the "Holder") is hereby granted the right to purchase at
any time  until  5:00  P.M.,  New York  City  time,  on  January  31,  2005 (the
"Expiration Date"),  Three Hundred Forty-seven Thousand Eight Hundred Twenty-six
(347,826) fully paid and nonassessable shares of the Company's Common Stock, par
value $.0001 per share (the  "Common  Stock") at an initial  exercise  price per
share  (the  "Exercise  Price'")  of  $3.4059  per  share,  subject  to  further
adjustment  asset forth  herein.  This Warrant is being  issued  pursuant to the
terms of that certain  Securities  Purchase  Agreement,  dated as of January 31,
2000 (the "Securities Purchase Agreement"),  to which the Company and Holder (or
Holder's  predecessor in interest) are parties.  Capitalized terms not otherwise
defined  herein  shall  have the  meanings  ascribed  to them in the  Securities
Purchase Agreement.

         2. Exercise of Warrants.

              2.1.  General.  This Warrant is exercisable in whole or in part at
any time and from time to time. Such exercise shall be effectuated by submitting
to the Company  (either by delivery to the Company or by facsimile  transmission
as  provided  in  Section 8  hereof) a  completed  and duly  executed  Notice of
Exercise  (substantially  in the form attached to this Warrant  Certificate)  as
provided  in this  paragraph.  The date such  Notice of Exercise is faxed to the
Company shall be the "Exercise  Date,"  provided that the Holder of this Warrant
tenders this Warrant  Certificate  to the Company  within five (5) business days
thereafter.  The  Notice of  Exercise  shall be  executed  by the Holder of this
Warrant and shall indicate the number of shares then being purchased pursuant to
such exercise.  Upon surrender of this Warrant  Certificate with,  together with
appropriate  payment  of the  Exercise  Price for the  shares  of  Common  Stock
purchased, the Holder shall be entitled to receive a certificate or certificates
for the shares of Common Stock so  purchased.  The  Exercise  Price per share of
Common Stock for the shares then being  exercised shall be payable in cash or by
certified  or  official  bank  check,  except that the Holder may apply all or a
portion of the previously  unapplied  aggregate Warrant Purchase Price specified
on the signature page of the Securities Purchase Agreement against the amount so
payable  pursuant to such exercise.  The Holder shall be deemed to be the holder
of the shares  issuable to it in accordance  with the provisions of this Section
2.1 on the Exercise Date.



              2.2.  Limitation on Exercise.  Notwithstanding  the  provisions of
this Warrant,  the  Securities  Purchase  Agreement or of the other  Transaction
Agreements,  in no event (except (i) after the Maturity Date of the  Debentures,
(ii) as specifically provided in this Warrant as an exception to this provision,
or (iii) while there is  outstanding a tender offer for any or all of the shares
of the  Company's  Common  Stock) shall the Holder be entitled to exercise  this
Warrant,  or shall the Company have either the  obligation  to issue shares upon
such  exercise of all or any portion of this Warrant or the right to require the
Holder to exercise this Warrant as  contemplated  by Section 2.3 hereof,  to the
extent that,  after such  exercise the sum of (1) the number of shares of Common
Stock  beneficially owned by the Holder and its affiliates (other than shares of
Common Stock which may be deemed beneficially owned through the ownership of the
unconverted  portion of the Debentures or unexercised  portion of the Warrants),
and (2) the number of shares of Common Stock  issuable  upon the exercise of the
Warrants with respect to which the  determination of this proviso is being made,
would result in  beneficial  ownership by the Holder and its  affiliates of more
than 9.99% of the outstanding  shares of Common Stock (after taking into account
the shares to be issued to the Holder upon such  exercise).  For purposes of the
proviso to the immediately  preceding  sentence,  beneficial  ownership shall be
determined in accordance  with Section 13(d) of the  Securities  Exchange Act of
1934, as amended (the "1934 Act"), except as otherwise provided in clause (1) of
such sentence.  The Holder,  by its  acceptance of this Warrant,  further agrees
that if the Holder  transfers  or assigns any of the  Warrants to a party who or
which would not be considered such an affiliate,  such assignment  shall be made
subject to the transferee's or assignee's  specific agreement to be bound by the
provisions  of this  Section  2.2 as if such  transferee  or  assignee  were the
original Holder hereof.

              2.3. Company Option to Require Exercise. If, but only if, both

              (i)  the Registration Statement is currently effective, and

              (ii) the  closing bid price for the Common  Stock,  as reported by
                   Bloomberg,  LP or, if not so  reported,  as  reported  by the
                   securities  exchange or automated  quotation  system on which
                   the Common Stock is listed or on the over-the-counter market,
                   for each of any fifteen (15)  consecutive  trading days is at
                   least two hundred  percent  (200%) of the Exercise  Price (as
                   the same may be adjusted as contemplated by the terms of this
                   Warrant),

the Company will have the right by written notice (the "Required Exercise
Notice") to the Holder to require the Holder to exercise all or a portion of the
unexercised portion of this Warrant in accordance with its terms (except that
such requirement shall not be deemed to require the Holder to exercise the
Warrant in a manner inconsistent with the provisions of Section 2.2 hereof). The
Company's right to issue a Required Exercise Notice shall expire at the close of
the fifth trading day after the last day in such consecutive trading day period
in which the closing bid price was at or above the standard referred to in
clause (ii) of this Section 2.3. The shares which are the subject of the
Required Exercise Notice are referred to as the "Required Shares." To the extent
the Holder does not exercise this Warrant for the Required Shares within five
(5) business days after the Holder's receipt of the Required Exercise Notice,
the Holder's rights under this Warrant with respect to the unexercised portion
of the Required Shares shall expire.

                                      -2-



         3.  Reservation of Shares.  The Company hereby agrees that at all times
during the term of this  Warrant  there  shall be  reserved  for  issuance  upon
exercise of this  Warrant  such number of shares of its Common Stock as shall be
required for issuance upon exercise of this Warrant (the "Warrant Shares").

         4.  Mutilation  or Loss of  Warrant.  Upon  receipt  by the  Company of
evidence  satisfactory  to it of the loss,  theft,  destruction or mutilation of
this  Warrant,  and (in the  case of  loss,  theft or  destruction)  receipt  of
reasonably  satisfactory  indemnification,  and (in the case of mutilation) upon
surrender and cancellation of this Warrant, the Company will execute and deliver
a new  Warrant of like tenor and date and any such lost,  stolen,  destroyed  or
mutilated Warrant shall thereupon become void.

         5. Rights of the Holder.  The Holder  shall not, by virtue  hereof,  be
entitled to any rights of a stockholder in the Company, either at law or equity,
and the rights of the Holder are limited to those  expressed in this Warrant and
are not enforceable against the Company except to the extent set forth herein.

         6. Protection Against Dilution.

              6.1. Adjustment Mechanism.  If an adjustment of the Exercise Price
is required pursuant to this Section 6, the Holder shall be entitled to purchase
such  number of  additional  shares of Common  Stock as will cause (i) the total
number of shares of Common Stock Holder is entitled to purchase pursuant to this
Warrant,  multiplied  by (ii) the adjusted  Exercise  Price per share,  to equal
(iii) the dollar  amount of the total number of shares of Common Stock Holder is
entitled to purchase  before  adjustment  multiplied by the total Exercise Price
before adjustment.

              6.2.  Capital  Adjustments.  In case of any stock split or reverse
stock   split,   stock   dividend,   reclassification   of  the  Common   Stock,
recapitalization,  merger or consolidation, or like capital adjustment affecting
the Common  Stock of the  Company,  the  provisions  of this  Section 6 shall be
applied as if such capital  adjustment event had occurred  immediately  prior to
the date of this  Warrant  and the  original  Exercise  Price  had  been  fairly
allocated  to the stock  resulting  from such capital  adjustment;  and in other
respects the  provisions of this Section  shall be applied in a fair,  equitable
and reasonable manner so as to give effect, as nearly as may be, to the purposes
hereof.  A rights offering to  stockholders  shall be deemed a stock dividend to
the extent of the bargain purchase element of the rights.

              6.3.  Adjustment  for Spin Off.  If, for any reason,  prior to the
exercise of this Warrant in full,  the Company  spins off or  otherwise  divests
itself of a part of its business or  operations  or disposes all or of a part of
its assets in a  transaction  (the  "Spin  Off') in which the  Company  does not
receive  compensation  for such  business,  operations  or  assets,  but  causes
securities  of  another  entity  (the  "Spin  Off  Securities")  to be issued to
security holders of the Company, then

              (a)  the  Company   shall  cause  (i)  to  be  reserved  Spin  Off
          Securities equal to the number thereof which would have been issued to
          the Holder had all of the Holder's unexercised Warrants outstanding on
          the record date (the  "Record  Date") for  determining

                                      -3-



          the amount and number of Spin Off  Securities to be issued to security
          holders of the Company (the "Outstanding  Warrants") been exercised as
          of the close of business on the  trading  day  immediately  before the
          Record Date (the "Reserved Spin Off Shares"), and (ii) to be issued to
          the Holder on the exercise of all or any of the Outstanding  Warrants,
          such amount of the Reserved  Spin Off Shares equal to (x) the Reserved
          Spin  Off  Shares  multiplied  by (y) a  fraction,  of  which  (I) the
          numerator  is  the  amount  of the  Outstanding  Warrants  then  being
          exercised,  and (I) the  denominator is the amount of the  Outstanding
          Warrants; and

              (b)  the  Exercise  Price  on the  Outstanding  Warrants  shall be
          adjusted immediately after consummation of the Spin Off by multiplying
          the Exercise  Price by a fraction  (if, but only if, such  fraction is
          less than 1.0),  the numerator of which is the Average Market Price of
          the Common  Stock (as  defined  below) for the five (5)  trading  days
          immediately following the fifth trading day after the Record Date, and
          the  denominator  of which is the Average  Market  Price of the Common
          Stock on the five (5) trading days  immediately  preceding  the Record
          Date;  and such  adjusted  Exercise  Price  shall be  deemed to be the
          Exercise  Price:  with respect to the  Outstanding  Warrants after the
          Record Date.  As used herein,  the term  "Average  Market Price of the
          Common Stock" means the average closing bid price of a share of Common
          Stock,  as  reported  by  Bloomberg,  LP or,  if not so  reported,  as
          reported on the over-the-counter market for the relevant period.

         7. Transfer to Comply with the Securities Act; Registration Rights.

              7.1.  Transfer.  This  Warrant has not been  registered  under the
Securities  Act of 1933,  as  amended,  (the  "Act") and has been  issued to the
Holder  for  investment  and not with a view to the  distribution  of either the
Warrant or the  Warrant  Shares.  Neither  this  Warrant  nor any of the Warrant
Shares or any other  security  issued or issuable  upon exercise of this Warrant
may be sold, transferred, pledged or hypothecated in the absence of an effective
registration  statement under the Act relating to such security or an opinion of
counsel  satisfactory to the Company that registration is not required under the
Act. Each certificate for the Warrant, the Warrant Shares and any other security
issued or issuable  upon  exercise of this Warrant shall contain a legend on the
face  thereof,  in form and substance  satisfactory  to counsel for the Company,
setting forth the restrictions on transfer contained in this Section.

              7.2.   Registration   Rights.   (a)   Reference  is  made  to  the
Registration Rights Agreement.  The Company's obligations under the Registration
Rights Agreement and the other terms and conditions  thereof with respect to the
Warrant  Shares,  including,  but not  necessarily  limited  to,  the  Company's
commitment to file a registration  statement  including the Warrant  Shares,  to
have the  registration  of the Warrant Shares  completed and  effective,  and to
maintain such registration, are incorporated herein by reference.

         (b) In addition to the registration rights referred to in the preceding
provisions  of  Section   7.2(a),   effective   after  the   expiration  of  the
effectiveness of the Registration  Statement as contemplated by the Registration
Rights  Agreement,  the Holder shall have  piggy-back  registration  rights with
respect  to the  Warrant  Shares  then  held by the  Holder or then  subject  to
issuance upon exercise of this Warrant  (collectively,  the  "Remaining  Warrant
Shares"),  subject

                                      -4-



to the  conditions  set  forth  below.  If, at any time  after the  Registration
Statement  has  ceased  to  be  effective,  the  Company  participates  (whether
voluntarily or by reason of an obligation to a third party) in the  registration
of any shares of the Company's  stock (other than a registration  on Form S-4 or
Form S-8),  the Company shall give written  notice thereof to the Holder and the
Holder shall have the right,  exercisable  within ten (10)  business  days after
receipt of such notice,  to demand inclusion of all or a portion of the Holder's
Remaining Warrant Shares in such registration statement. If the Holder exercises
such election,  the Remaining  Warrant Shares so designated shall be included in
the  registration  statement at no cost or expense to the Holder (other than any
costs or  commissions  which would be borne by the Holder under the terms of the
Registration  Rights Agreement).  The Holder's rights under this Section 7 shall
expire at such time as the Holder can sell all of the Remaining  Warrant  Shares
under Rule 144 without volume or other restrictions or limit.

         8.  Notices.  Any notice or other  communication  required or permitted
hereunder  shall be in writing and shall be delivered  personally,  telegraphed,
telexed,  sent by facsimile  transmission  or sent by  certified,  registered or
express mail,  postage  pre-paid.  Any such notice shall be deemed given when so
delivered personally,  telegraphed,  telexed or sent by facsimile  transmission,
or, if mailed, two days after the date of deposit in the United States mails, as
follows:

              (i)           if to the Company, to:

                            Siga Pharmaceuticals, Inc.
                            420 Lexington Avenue, Suite 620
                            New York, New York 10170
                            Attn:  Judson Cooper
                            Telephone No.: (212) 672-9150
                            Telecopier No.: (212) 697-3130

                            and with a copy to:

                            Orrick Herrington & Sutcliffe, LLP
                            666 Fifth Avenue
                            New York, NY 10103
                            Attn:  Jeffrey Fessler, Esq.
                            Telephone No.: (212) 506-5000
                            Telecopier No.: (212) 506-5151

              (ii)          if to the Holder, to:

                            Donald G. Drapkin
                            c/o 35 East 62nd Street
                            New York, NY 10021-8016
                            Telephone No.:  (    ) ___-____
                            Telecopier No.: (212) 572-5184

                                      -5-



                            with a copy to:

                            Krieger & Prager LLP, Esqs.
                            39 Broadway
                            Suite 1440
                            New York, NY 10006
                            Attn: Samuel Krieger, Esq.
                            Telephone No.: (212) 363-2900
                            Telecopier No. (212) 363-2999

Any party may be notice given in accordance with this Section to the other
parties designate another address or person for receipt of notices hereunder.

         9.  Supplements and Amendments;  Whole  Agreement.  This Warrant may be
amended or  supplemented  only by an instrument in writing signed by the parties
hereto. This Warrant of even date herewith contain the full understanding of the
parties  hereto with respect to the subject  matter hereof and thereof and there
are no  representations,  warranties,  agreements or  understandings  other than
expressly contained herein and therein.

         10.  Governing  Law. This Warrant shall be deemed to be a contract made
under the laws of the State of New York for contracts to be wholly  performed in
such state and without  giving effect to the  principles  thereof  regarding the
conflict  of laws.  Each of the  parties  consents  to the  jurisdiction  of the
federal courts whose districts encompass any part of the City of New York or the
state  courts  of the  State  of New  York  sitting  in the  City of New York in
connection with any dispute arising under this Warrant and hereby waives, to the
maximum extent permitted by law, any objection, including any objection based on
forum  non  conveniens,   to  the  bringing  of  any  such  proceeding  in  such
jurisdictions.  To the  extent  determined  by such  court,  the  Company  shall
reimburse the Holder for any reasonable legal fees and disbursements incurred by
the Buyer in  enforcement of or protection of any of its rights under any of the
Transaction Agreements.

         11.  Counterparts.  This  Warrant  may be  executed  in any  number  of
counterparts and each of such  counterparts  shall for all purposes be deemed to
be an original,  and all such counterparts shall together constitute but one and
the same instrument.


                                      -6-



         12. Descriptive Headings.  Descriptive headings of the several Sections
of this  Warrant  are  inserted  for  convenience  only and shall not control or
affect the meaning or construction of any of the provisions hereof.

      IN WITNESS WHEREOF, the parties hereto have executed this Warrant as of
the 31th day of January, 2000.

                                    SIGA PHARMACEUTICALS, INC.


                                    By: /s/ Judson Cooper
                                       ---------------------------
                                    Name: Judson Cooper
                                    Its:  Chairman

Attest:


/s/ Joshua D. Schein
- ------------------------------
Name:  Joshua D. Schein
Title: CEO


                                      -7-



                          NOTICE OF EXERCISE OF WARRANT

      The undersigned hereby irrevocably elects to exercise the right,
represented by the Warrant Certificate dated as of _________________, ___, to
purchase shares of the Common Stock, par value $.0001 per share, of SIGA
PHARMACEUTICALS, INC. and tenders herewith payment in accordance with Section 1
of said Common Stock Purchase Warrant.

      Please deliver the stock certificate to:







Dated:
      __________________________



________________________________
[Name of Holder]



By:_____________________________


|_|   CASH:                                     $__________________

      Less:  CREDIT FOR PREVIOUSLY
      UNAPPLIED WARRANT PURCHASE PRICE:

                                                $-------------------

      CURRENT PAYMENT:                          $___________________



                                      -8-



                                                                       Exhibit E

      THESE SECURITIES INCLUDING ANY UNDERLYING SECURITIES (THE "SECURITIES")
      HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
      THE SECURITIES LAWS OF ANY STATE AND MAY NOT BE SOLD OR OFFERED FOR SALE
      IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES
      OR AN OPINION OF COUNSEL OR OTHER EVIDENCE ACCEPTABLE TO THE COMPANY THAT
      SUCH REGISTRATION IS NOT REQUIRED.

                           SIGA PHARMACEUTICALS, INC.

                          COMMON STOCK PURCHASE WARRANT

         1. Issuance; Certain Definitions. In consideration of good and valuable
consideration,   the   receipt   of  which  is  hereby   acknowledged   by  SIGA
PHARMACEUTICALS,  INC.,  a  Delaware  corporation  (the  "Company"),  GABRIEL M.
CERRONE or  registered  assigns (the  "Holder")  is hereby  granted the right to
purchase  at any time until 5:00 P.M.,  New York City time,  on January 31, 2005
(the  "Expiration  Date"),  Two Hundred Ten  Thousand  (210,000)  fully paid and
nonassessable  shares of the Company's  Common Stock, par value $.0001 per share
(the  "Common  Stock") at an  initial  exercise  price per share (the  "Exercise
Price") of $1.45 per share,  subject to further  adjustment as set forth herein.
Reference is made to that certain  Securities  Purchase  Agreement,  dated as of
January 31, 2000 (the "Securities Purchase Agreement"), to which the Company and
certain named Buyers are parties. Capitalized terms not otherwise defined herein
shall have the meanings ascribed to them in the Securities Purchase Agreement.

         2. Exercise of Warrants.

            2.1 General.  This Warrant is exercisable in whole or in part at any
time and from time to time.  Such exercise shall be effectuated by submitting to
the Company  (either by delivery to the Company or by facsimile  transmission as
provided in Section 8 hereof) a completed and duly  executed  Notice of Exercise
(substantially in the form attached to this Warrant  Certificate) as provided in
this  paragraph.  The date such Notice of Exercise is faxed to the Company shall
be the "Exercise  Date,"  provided that the Holder of this Warrant  tenders this
Warrant Certificate to the Company within five (5) business days thereafter. The
Notice of Exercise  shall be  executed  by the Holder of this  Warrant and shall
indicate the number of shares then being  purchased  pursuant to such  exercise.
Upon  surrender of this Warrant  Certificate  with,  together  with  appropriate
payment of the  Exercise  Price for the shares of Common  Stock  purchased,  the
Holder shall be entitled to receive a certificate or certificates for the shares
of Common Stock so purchased.  The Exercise  Price per share of Common Stock for
the shares  then being  exercised  shall be payable in cash or by  certified  or
official  bank check.  The Holder shall be deemed to be the holder of the shares
issuable to it in  accordance  with the  provisions  of this  Section 2.1 on the
Exercise Date.

            2.2 Limitation on Exercise.  Notwithstanding  the provisions of this
Warrant, in no event (except (i) as specifically  provided in this Warrant as an
exception to this  provision,  or (ii) while there is outstanding a tender offer
for any or all of the shares of the



Company's  Common  Stock) shall the Holder be entitled to exercise this Warrant,
or shall the  Company  have  either the  obligation  to issue  shares  upon such
exercise of all or any portion of this Warrant,  to the extent that,  after such
exercise the sum of (1) the number of shares of Common Stock  beneficially owned
by the Holder and its affiliates (other than shares of Common Stock which may be
deemed  beneficially  owned through the ownership of the unexercised  portion of
the  Warrants),  and (2) the number of shares of Common Stock  issuable upon the
exercise of the Warrants with respect to which the determination of this proviso
is being  made,  would  result in  beneficial  ownership  by the  Holder and its
affiliates of more than 9.99% of the  outstanding  shares of Common Stock (after
taking into  account the shares to be issued to the Holder upon such  exercise).
For purposes of the proviso to the immediately  preceding  sentence,  beneficial
ownership shall be determined in accordance with Section 13(d) of the Securities
Exchange Act of 1934, as amended (the "1934 Act"),  except as otherwise provided
in clause (1) of such sentence.  The Holder,  by its acceptance of this Warrant,
further agrees that if the Holder  transfers or assigns any of the Warrants to a
party who or which would not be considered  such an affiliate,  such  assignment
shall be made subject to the transferee's or assignee's specific agreement to be
bound by the  provisions  of this Section 2.2 as if such  transferee or assignee
were the original Holder hereof.

         3.  Reservation of Shares.  The Company hereby agrees that at all times
during the term of this  Warrant  there  shall be  reserved  for  issuance  upon
exercise of this  Warrant  such number of shares of its Common Stock as shall be
required for issuance upon exercise of this Warrant (the "Warrant Shares").

         4.  Mutilation  or Loss of  Warrant.  Upon  receipt  by the  Company of
evidence  satisfactory  to it of the loss,  theft,  destruction or mutilation of
this  Warrant,  and (in the  case of  loss,  theft or  destruction)  receipt  of
reasonably  satisfactory  indemnification,  and (in the case of mutilation) upon
surrender and cancellation of this Warrant, the Company will execute and deliver
a new  Warrant of like tenor and date and any such lost,  stolen,  destroyed  or
mutilated Warrant shall thereupon become void.

         5. Rights of the Holder.  The Holder  shall not, by virtue  hereof,  be
entitled to any rights of a stockholder in the Company, either at law or equity,
and the rights of the Holder and limited to those  expressed in this Warrant and
are not enforceable against the Company except to the extent set forth herein.

         6. Protection Against Dilution.

            6.1 Adjustment Mechanism.  If an adjustment of the Exercise Price is
required  pursuant to this  Section 6, the Holder  shall be entitled to purchase
such  number of  additional  shares of Common  Stock as will cause (i) the total
number of shares of Common Stock Holder is entitled to purchase pursuant to this
Warrant,  multiplied  by (ii) the adjusted  Exercise  Price per share,  to equal
(iii) the dollar  amount of the total number of shares of Common Stock Holder is
entitled to purchase  before  adjustment  multiplied by the total Exercise Price
before adjustment.

            6.2 Capital Adjustments. In case of any stock split or reverse stock
split, stock dividend,  reclassification of the Common Stock,  recapitalization,
merger or

                                      -2-



consolidation,  or like  capital  adjustment  affecting  the Common Stock of the
Company,  the  provisions  of this Section 6 shall be applied as if such capital
adjustment event had occurred  immediately prior to the date of this Warrant and
the original  Exercise  Price had been fairly  allocated to the stock  resulting
from such  capital  adjustment;  and in other  respects the  provisions  of this
Section  shall be applied in a fair,  equitable and  reasonable  manner so as to
give effect,  as nearly as may be, to the purposes  hereof. A rights offering to
stockholders  shall be deemed a stock  dividend  to the  extent  of the  bargain
purchase element of the rights.

            6.3  Adjustment  for Spin  Off.  If,  for any  reason,  prior to the
exercise of this Warrant in full,  the Company  spins off or  otherwise  divests
itself of a part of its business or  operations  or disposes all or of a part of
its assets in a  transaction  (the  "Spin  Off") in which the  Company  does not
receive  compensation  for such  business,  operations  or  assets,  but  causes
securities  of  another  entity  (the  "Spin  Off  Securities")  to be issued to
security holders of the Company, then

             (a) the Company shall cause (i) to be reserved Spin Off  Securities
      equal to the number thereof which would have been issued to the Holder had
      all of the Holder's  unexercised  Warrants  outstanding on the record date
      (the  "Record  Date")  for  determining  the amount and number of Spin Off
      Securities  to  be  issued  to  security   holders  of  the  Company  (the
      "Outstanding  Warrants") been exercised as of the close of business on the
      trading day  immediately  before the Record Date (the  "Reserved  Spin Off
      Shares"),  and (ii) to be issued to the Holder on the  exercise  of all or
      any of the  Outstanding  Warrants,  such amount of the  Reserved  Spin Off
      Shares  equal to (x) the  Reserved  Spin Off  Shares  multiplied  by (y) a
      fraction,  of which (I) the  numerator  is the  amount of the  Outstanding
      Warrants then being  exercised,  and (II) the denominator is the amount of
      the Outstanding Warrants; and

             (b)  the  Exercise  Price  on the  Outstanding  Warrants  shall  be
      adjusted immediately after consummation of the Spin Off by multiplying the
      Exercise  Price by a fraction (if, but only if, such fraction is less than
      1.0),  the  numerator  of which is the Average  Market Price of the Common
      Stock  (as  defined  below)  for the five  (5)  trading  days  immediately
      following the fifth trading day after the Record Date, and the denominator
      of which is the Average  Market  Price of the Common Stock on the five (5)
      trading days  immediately  preceding  the Record Date;  and such  adjusted
      Exercise  Price shall be deemed to be the  Exercise  Price with respect to
      the Outstanding  Warrants after the Record Date. As used herein,  the term
      "Average  Market Price of the Common Stock" means the average  closing bid
      price of a share of Common Stock, as reported by Bloomberg,  LP or, if not
      so reported,  as reported on the over-the-counter  market for the relevant
      period.

         7. Transfer to Comply with the Securities Act; Registration Rights.

            7.1  Transfer.  This  Warrant  has not  been  registered  under  the
Securities Act of 1933, as amended (the "Act") and has been issued to the Holder
for investment and not with a view to the  distribution of either the Warrant or
the Warrant  Shares.  Neither this Warrant nor any of the Warrant  Shares or any
other  security  issued or issuable  upon  exercise of this Warrant may be sold,
transferred, pledged or hypothecated in the absence of an effective

                                      -3-



registration  statement under the Act relating to such security or an opinion of
counsel  satisfactory to the Company that registration is not required under the
Act. Each certificate for the Warrant, the Warrant Shares and any other security
issued or issuable  upon  exercise of this Warrant shall contain a legend on the
face  thereof,  in form and substance  satisfactory  to counsel for the Company,
setting forth the restrictions on transfer contained in this Section.

            7.2 Registration  Rights.  (a) Reference is made to the Registration
Rights  Agreement,  dated  January  31,  2000,  to which the Company and certain
Initial   Investors  named  therein  are  parties  (the   "Registration   Rights
Agreement").  The  shares  issuable  upon  exercise  of this  Warrant  ("Warrant
Shares") are Registrable  Securities,  as that term is used in the  Registration
Rights  Agreement.  Subject  to and in  accordance  with the  provisions  of the
Registration  Rights  Agreement (the terms of which are  incorporated  herein by
reference),  the Company agrees to file a registration statement or an amendment
to its registration statement on Form S-3 which shall include the Warrant Shares
(as so filed or amended, the "Registration Statement"),  pursuant to the Act, by
the  Required  Filing Date and to have the  registration  of the Warrant  Shares
completed  and  effective  by the  Required  Effective  Date (as those terms are
defined in the Registration Rights Agreement) and to maintain such registration.

         (b) In addition to the registration rights referred to in the preceding
provisions  of  Section   7.2(a),   effective   after  the   expiration  of  the
effectiveness of the Registration  Statement as contemplated by the Registration
Rights  Agreement,  the Holder shall have  piggy-back  registration  rights with
respect  to the  Warrant  Shares  then  held by the  Holder or then  subject  to
issuance upon exercise of this Warrant  (collectively,  the  "Remaining  Warrant
Shares),  subject to the conditions  set forth below.  If, at any time after the
New Registration Statement has ceased to be effective,  the Company participates
(whether  voluntarily  or by reason of an  obligation  to a third  party) in the
registration  of any shares of the Company's stock (other than a registration on
Form S-4 or Form S-8),  the Company  shall give  written  notice  thereof to the
Holder and the Holder shall have the right, exercisable within ten (10) business
days after  receipt of such notice,  to demand  inclusion of all or a portion of
the Holder's  Remaining  Warrant Shares in such registration  statement.  If the
Holder exercises such election, the Remaining Warrant Shares so designated shall
be included in the  registration  statement  at no cost or expense to the Holder
(other than any costs or  commissions  which would be borne by the Holder  under
the terms of the Registration Rights Agreement).

         8.  Notices.  Any notice or other  communication  required or permitted
hereunder  shall be in writing and shall be delivered  personally,  telegraphed,
telexed,  sent by facsimile  transmission  or sent by  certified,  registered or
express mail,  postage  pre-paid.  Any such notice shall be deemed given when so
delivered personally,  telegraphed,  telexed or sent by facsimile  transmission,
or, if mailed, two days after the date of deposit in the United States mails, as
follows:

               (i)      if to the Company, to;

                        Siga Pharmaceuticals, Inc.
                        420 Lexington Avenue, Suite 620
                        New York, New York 10170
                        Attn:  Judson Cooper
                        Telephone No.:  (212) 672-9150
                        Telecopier No.:  (212) 697-3130

                                      -4-



                        and with a copy to:

                        Orrick Herrington & Sutcliffe, LLP
                        666 Fifth Avenue
                        New York, NY 10103
                        Attn:  Jeffrey Fessler, Esq.
                        Telephone No.:  (212) 506-5000
                        Telecopier No.:  (212) 506-5151


               (ii)     if to the Holder, to:

                        Gabriel M. Cerrone
                        265 E. 66th St.
                        Apt. 16G
                        New York, NY 10021
                        Telephone No.:  (212) 755-6003
                        Telecopier No.:  (212) 755-6574

                        with a copy to:

                        Krieger & Prager LLP, Esqs.
                        39 Broadway
                        Suite 1440
                        New York, NY 10006
                        Attn:  Samuel Krieger, Esq.
                        Telephone No.:  (212) 363-2900
                        Telecopier No.:  (212) 363-2999

Any party may be notice given in accordance with this Section to the other
parties designate another address or person for receipt of notices hereunder.

         9.  Supplements and Amendments;  Whole  Agreement.  This Warrant may be
amended or  supplemented  only by an instrument in writing signed by the parties
hereto. This Warrant of even date herewith contain the full understanding of the
parties  hereto with respect to the subject  matter hereof and thereof and there
are no  representations,  warranties,  agreements or  understandings  other than
expressly contained herein and therein.

         10.  Governing  Law. This Warrant shall be deemed to be a contract made
under the laws of the State of New York for contracts to be wholly  performed in
such state and without  giving effect to the  principles  thereof  regarding the
conflict  of laws.  Each of the  parties  consents  to the  jurisdiction  of the
federal courts whose districts encompass any part of the City of New York or the
state  courts  of the  State  of New  York  sitting  in the  City of New York in
connection with any dispute arising under this Warrant and hereby waives, to the
maximum

                                      -5-



extent  permitted by law, any objection,  including any objection based on forum
non conveniens, to the bringing of any such proceeding in such jurisdictions. To
the extent  determined by such court, the Company shall reimburse the Holder for
any reasonable legal fees and disbursements incurred by the Buyer in enforcement
of or protection of any of its rights under any of the Transaction Agreements.

         11.  Counterparts.  This  Warrant  may be  executed  in any  number  of
counterparts and each of such  counterparts  shall for all purposes be deemed to
be an original,  and all such counterparts shall together constitute but one and
the same instrument.

         12. Descriptive Headings.  Descriptive headings of the several Sections
of this  Warrant  are  inserted  for  convenience  only and shall not control or
affect the meaning or construction of any of the provisions hereof.

         IN WITNESS WHEREOF, the parties hereto have executed this Warrant as of
the __th day of ___________, 2000.

                                    SIGA PHARMACEUTICALS, INC.


                                    By:
                                        --------------------------------------
                                        Name:
                                               -------------------------------
                                        Its:
                                              --------------------------------



Attest:



Name:
       -----------------------------
Title:
        ----------------------------


                                      -6-



                          NOTICE OF EXERCISE OF WARRANT

         The  undersigned  hereby  irrevocably  elects to  exercise  the  right,
represented by the Warrant  Certificate  dated as  of______________,  _____,  to
purchase  shares of the  Common  Stock,  par value  $.0001  per  share,  of SIGA
TECHNOLOGIES,  INC. and tenders herewith payment in accordance with Section 1 of
said Common Stock Purchase Warrant.

         Please deliver the stock certificate to:




Dated:___________________________




[Name of Holder]



By:


[ ]     CASH:                              $____________________




                                                                       Exhibit F

      THESE SECURITIES INCLUDING ANY UNDERLYING SECURITIES (THE "SECURITIES")
      HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
      THE SECURITIES LAWS OF ANY STATE AND MAY NOT BE SOLD OR OFFERED FOR SALE
      IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES
      OR AN OPINION OF COUNSEL OR OTHER EVIDENCE ACCEPTABLE TO THE COMPANY THAT
      SUCH REGISTRATION IS NOT REQUIRED.

                           SIGA PHARMACEUTICALS, INC.

                          COMMON STOCK PURCHASE WARRANT

         1. Issuance; Certain Definitions. In consideration of good and valuable
consideration,   the   receipt   of  which  is  hereby   acknowledged   by  SIGA
PHARMACEUTICALS,  INC.,  a  Delaware  corporation  (the  "Company"),  GABRIEL M.
CERRONE or  registered  assigns (the  "Holder")  is hereby  granted the right to
purchase  at any time until 5:00 P.M.,  New York City time,  on January 31, 2005
(the  "Expiration  Date"),  Two Hundred Ten  Thousand  (210,000)  fully paid and
nonassessable  shares of the Company's  Common Stock, par value $.0001 per share
(the  "Common  Stock") at an  initial  exercise  price per share (the  "Exercise
Price") of $1.45 per share,  subject to further  adjustment as set forth herein.
Reference is made to that certain  Securities  Purchase  Agreement,  dated as of
January 31, 2000 (the "Securities Purchase Agreement"), to which the Company and
certain named Buyers are parties. Capitalized terms not otherwise defined herein
shall have the meanings ascribed to them in the Securities Purchase Agreement.

         2. Exercise of Warrants.

            2.1 General.  This Warrant is exercisable in whole or in part at any
time and from time to time.  Such exercise shall be effectuated by submitting to
the Company  (either by delivery to the Company or by facsimile  transmission as
provided in Section 8 hereof) a completed and duly  executed  Notice of Exercise
(substantially in the form attached to this Warrant  Certificate) as provided in
this  paragraph.  The date such Notice of Exercise is faxed to the Company shall
be the "Exercise  Date,"  provided that the Holder of this Warrant  tenders this
Warrant Certificate to the Company within five (5) business days thereafter. The
Notice of Exercise  shall be  executed  by the Holder of this  Warrant and shall
indicate the number of shares then being  purchased  pursuant to such  exercise.
Upon  surrender of this Warrant  Certificate  with,  together  with  appropriate
payment of the  Exercise  Price for the shares of Common  Stock  purchased,  the
Holder shall be entitled to receive a certificate or certificates for the shares
of Common Stock so purchased.  The Exercise  Price per share of Common Stock for
the shares  then being  exercised  shall be payable in cash or by  certified  or
official  bank check.  The Holder shall be deemed to be the holder of the shares
issuable to it in  accordance  with the  provisions  of this  Section 2.1 on the
Exercise Date.

            2.2 Limitation on Exercise.  Notwithstanding  the provisions of this
Warrant, in no event (except (i) as specifically  provided in this Warrant as an
exception to this  provision,  or (ii) while there is outstanding a tender offer
for any or all of the shares of the



Company's  Common  Stock) shall the Holder be entitled to exercise this Warrant,
or shall the  Company  have  either the  obligation  to issue  shares  upon such
exercise of all or any portion of this Warrant,  to the extent that,  after such
exercise the sum of (1) the number of shares of Common Stock  beneficially owned
by the Holder and its affiliates (other than shares of Common Stock which may be
deemed  beneficially  owned through the ownership of the unexercised  portion of
the  Warrants),  and (2) the number of shares of Common Stock  issuable upon the
exercise of the Warrants with respect to which the determination of this proviso
is being  made,  would  result in  beneficial  ownership  by the  Holder and its
affiliates of more than 9.99% of the  outstanding  shares of Common Stock (after
taking into  account the shares to be issued to the Holder upon such  exercise).
For purposes of the proviso to the immediately  preceding  sentence,  beneficial
ownership shall be determined in accordance with Section 13(d) of the Securities
Exchange Act of 1934, as amended (the "1934 Act"),  except as otherwise provided
in clause (1) of such sentence.  The Holder,  by its acceptance of this Warrant,
further agrees that if the Holder  transfers or assigns any of the Warrants to a
party who or which would not be considered  such an affiliate,  such  assignment
shall be made subject to the transferee's or assignee's specific agreement to be
bound by the  provisions  of this Section 2.2 as if such  transferee or assignee
were the original Holder hereof.

         3.  Reservation of Shares.  The Company hereby agrees that at all times
during the term of this  Warrant  there  shall be  reserved  for  issuance  upon
exercise of this  Warrant  such number of shares of its Common Stock as shall be
required for issuance upon exercise of this Warrant (the "Warrant Shares").

         4.  Mutilation  or Loss of  Warrant.  Upon  receipt  by the  Company of
evidence  satisfactory  to it of the loss,  theft,  destruction or mutilation of
this  Warrant,  and (in the  case of  loss,  theft or  destruction)  receipt  of
reasonably  satisfactory  indemnification,  and (in the case of mutilation) upon
surrender and cancellation of this Warrant, the Company will execute and deliver
a new  Warrant of like tenor and date and any such lost,  stolen,  destroyed  or
mutilated Warrant shall thereupon become void.

         5. Rights of the Holder.  The Holder  shall not, by virtue  hereof,  be
entitled to any rights of a stockholder in the Company, either at law or equity,
and the rights of the Holder and limited to those  expressed in this Warrant and
are not enforceable against the Company except to the extent set forth herein.

         6. Protection Against Dilution.

            6.1 Adjustment Mechanism.  If an adjustment of the Exercise Price is
required  pursuant to this  Section 6, the Holder  shall be entitled to purchase
such  number of  additional  shares of Common  Stock as will cause (i) the total
number of shares of Common Stock Holder is entitled to purchase pursuant to this
Warrant,  multiplied  by (ii) the adjusted  Exercise  Price per share,  to equal
(iii) the dollar  amount of the total number of shares of Common Stock Holder is
entitled to purchase  before  adjustment  multiplied by the total Exercise Price
before adjustment.

            6.2 Capital Adjustments. In case of any stock split or reverse stock
split, stock dividend,  reclassification of the Common Stock,  recapitalization,
merger or

                                      -2-



consolidation,  or like  capital  adjustment  affecting  the Common Stock of the
Company,  the  provisions  of this Section 6 shall be applied as if such capital
adjustment event had occurred  immediately prior to the date of this Warrant and
the original  Exercise  Price had been fairly  allocated to the stock  resulting
from such  capital  adjustment;  and in other  respects the  provisions  of this
Section  shall be applied in a fair,  equitable and  reasonable  manner so as to
give effect,  as nearly as may be, to the purposes  hereof. A rights offering to
stockholders  shall be deemed a stock  dividend  to the  extent  of the  bargain
purchase element of the rights.

            6.3  Adjustment  for Spin  Off.  If,  for any  reason,  prior to the
exercise of this Warrant in full,  the Company  spins off or  otherwise  divests
itself of a part of its business or  operations  or disposes all or of a part of
its assets in a  transaction  (the  "Spin  Off") in which the  Company  does not
receive  compensation  for such  business,  operations  or  assets,  but  causes
securities  of  another  entity  (the  "Spin  Off  Securities")  to be issued to
security holders of the Company, then

             (a) the Company shall cause (i) to be reserved Spin Off  Securities
      equal to the number thereof which would have been issued to the Holder had
      all of the Holder's  unexercised  Warrants  outstanding on the record date
      (the  "Record  Date")  for  determining  the amount and number of Spin Off
      Securities  to  be  issued  to  security   holders  of  the  Company  (the
      "Outstanding  Warrants") been exercised as of the close of business on the
      trading day  immediately  before the Record Date (the  "Reserved  Spin Off
      Shares"),  and (ii) to be issued to the Holder on the  exercise  of all or
      any of the  Outstanding  Warrants,  such amount of the  Reserved  Spin Off
      Shares  equal to (x) the  Reserved  Spin Off  Shares  multiplied  by (y) a
      fraction,  of which (I) the  numerator  is the  amount of the  Outstanding
      Warrants then being  exercised,  and (II) the denominator is the amount of
      the Outstanding Warrants; and

             (b)  the  Exercise  Price  on the  Outstanding  Warrants  shall  be
      adjusted immediately after consummation of the Spin Off by multiplying the
      Exercise  Price by a fraction (if, but only if, such fraction is less than
      1.0),  the  numerator  of which is the Average  Market Price of the Common
      Stock  (as  defined  below)  for the five  (5)  trading  days  immediately
      following the fifth trading day after the Record Date, and the denominator
      of which is the Average  Market  Price of the Common Stock on the five (5)
      trading days  immediately  preceding  the Record Date;  and such  adjusted
      Exercise  Price shall be deemed to be the  Exercise  Price with respect to
      the Outstanding  Warrants after the Record Date. As used herein,  the term
      "Average  Market Price of the Common Stock" means the average  closing bid
      price of a share of Common Stock, as reported by Bloomberg,  LP or, if not
      so reported,  as reported on the over-the-counter  market for the relevant
      period.

         7. Transfer to Comply with the Securities Act; Registration Rights.

            7.1  Transfer.  This  Warrant  has not  been  registered  under  the
Securities Act of 1933, as amended (the "Act") and has been issued to the Holder
for investment and not with a view to the  distribution of either the Warrant or
the Warrant  Shares.  Neither this Warrant nor any of the Warrant  Shares or any
other  security  issued or issuable  upon  exercise of this Warrant may be sold,
transferred, pledged or hypothecated in the absence of an effective

                                      -3-



registration  statement under the Act relating to such security or an opinion of
counsel  satisfactory to the Company that registration is not required under the
Act. Each certificate for the Warrant, the Warrant Shares and any other security
issued or issuable  upon  exercise of this Warrant shall contain a legend on the
face  thereof,  in form and substance  satisfactory  to counsel for the Company,
setting forth the restrictions on transfer contained in this Section.

            7.2 Registration  Rights.  (a) Reference is made to the Registration
Rights  Agreement,  dated  January  31,  2000,  to which the Company and certain
Initial   Investors  named  therein  are  parties  (the   "Registration   Rights
Agreement").  The  shares  issuable  upon  exercise  of this  Warrant  ("Warrant
Shares") are Registrable  Securities,  as that term is used in the  Registration
Rights  Agreement.  Subject  to and in  accordance  with the  provisions  of the
Registration  Rights  Agreement (the terms of which are  incorporated  herein by
reference),  the Company agrees to file a registration statement or an amendment
to its registration statement on Form S-3 which shall include the Warrant Shares
(as so filed or amended, the "Registration Statement"),  pursuant to the Act, by
the  Required  Filing Date and to have the  registration  of the Warrant  Shares
completed  and  effective  by the  Required  Effective  Date (as those terms are
defined in the Registration Rights Agreement) and to maintain such registration.

         (b) In addition to the registration rights referred to in the preceding
provisions  of  Section   7.2(a),   effective   after  the   expiration  of  the
effectiveness of the Registration  Statement as contemplated by the Registration
Rights  Agreement,  the Holder shall have  piggy-back  registration  rights with
respect  to the  Warrant  Shares  then  held by the  Holder or then  subject  to
issuance upon exercise of this Warrant  (collectively,  the  "Remaining  Warrant
Shares),  subject to the conditions  set forth below.  If, at any time after the
New Registration Statement has ceased to be effective,  the Company participates
(whether  voluntarily  or by reason of an  obligation  to a third  party) in the
registration  of any shares of the Company's stock (other than a registration on
Form S-4 or Form S-8),  the Company  shall give  written  notice  thereof to the
Holder and the Holder shall have the right, exercisable within ten (10) business
days after  receipt of such notice,  to demand  inclusion of all or a portion of
the Holder's  Remaining  Warrant Shares in such registration  statement.  If the
Holder exercises such election, the Remaining Warrant Shares so designated shall
be included in the  registration  statement  at no cost or expense to the Holder
(other than any costs or  commissions  which would be borne by the Holder  under
the terms of the Registration Rights Agreement).

         8.  Notices.  Any notice or other  communication  required or permitted
hereunder  shall be in writing and shall be delivered  personally,  telegraphed,
telexed,  sent by facsimile  transmission  or sent by  certified,  registered or
express mail,  postage  pre-paid.  Any such notice shall be deemed given when so
delivered personally,  telegraphed,  telexed or sent by facsimile  transmission,
or, if mailed, two days after the date of deposit in the United States mails, as
follows:

               (i)      if to the Company, to;

                        Siga Pharmaceuticals, Inc.
                        420 Lexington Avenue, Suite 620
                        New York, New York 10170
                        Attn:  Judson Cooper
                        Telephone No.:  (212) 672-9150
                        Telecopier No.:  (212) 697-3130

                                      -4-



                        and with a copy to:

                        Orrick Herrington & Sutcliffe, LLP
                        666 Fifth Avenue
                        New York, NY 10103
                        Attn:  Jeffrey Fessler, Esq.
                        Telephone No.:  (212) 506-5000
                        Telecopier No.:  (212) 506-5151


               (ii)     if to the Holder, to:

                        Gabriel M. Cerrone
                        265 E. 66th St.
                        Apt. 16G
                        New York, NY 10021
                        Telephone No.:  (212) 755-6003
                        Telecopier No.:  (212) 755-6574

                        with a copy to:

                        Krieger & Prager LLP, Esqs.
                        39 Broadway
                        Suite 1440
                        New York, NY 10006
                        Attn:  Samuel Krieger, Esq.
                        Telephone No.:  (212) 363-2900
                        Telecopier No.:  (212) 363-2999

Any party may be notice given in accordance with this Section to the other
parties designate another address or person for receipt of notices hereunder.

         9.  Supplements and Amendments;  Whole  Agreement.  This Warrant may be
amended or  supplemented  only by an instrument in writing signed by the parties
hereto. This Warrant of even date herewith contain the full understanding of the
parties  hereto with respect to the subject  matter hereof and thereof and there
are no  representations,  warranties,  agreements or  understandings  other than
expressly contained herein and therein.

         10.  Governing  Law. This Warrant shall be deemed to be a contract made
under the laws of the State of New York for contracts to be wholly  performed in
such state and without  giving effect to the  principles  thereof  regarding the
conflict  of laws.  Each of the  parties  consents  to the  jurisdiction  of the
federal courts whose districts encompass any part of the City of New York or the
state  courts  of the  State  of New  York  sitting  in the  City of New York in
connection with any dispute arising under this Warrant and hereby waives, to the
maximum

                                      -5-



extent  permitted by law, any objection,  including any objection based on forum
non conveniens, to the bringing of any such proceeding in such jurisdictions. To
the extent  determined by such court, the Company shall reimburse the Holder for
any reasonable legal fees and disbursements incurred by the Buyer in enforcement
of or protection of any of its rights under any of the Transaction Agreements.

         11.  Counterparts.  This  Warrant  may be  executed  in any  number  of
counterparts and each of such  counterparts  shall for all purposes be deemed to
be an original,  and all such counterparts shall together constitute but one and
the same instrument.

         12. Descriptive Headings.  Descriptive headings of the several Sections
of this  Warrant  are  inserted  for  convenience  only and shall not control or
affect the meaning or construction of any of the provisions hereof.

         IN WITNESS WHEREOF, the parties hereto have executed this Warrant as of
the __th day of ___________, 2000.

                                    SIGA PHARMACEUTICALS, INC.


                                    By:
                                        --------------------------------------
                                        Name:
                                               -------------------------------
                                        Its:
                                              --------------------------------



Attest:



Name:
       -----------------------------
Title:
        ----------------------------


                                      -6-



                          NOTICE OF EXERCISE OF WARRANT

         The  undersigned  hereby  irrevocably  elects to  exercise  the  right,
represented by the Warrant  Certificate  dated as  of______________,  _____,  to
purchase  shares of the  Common  Stock,  par value  $.0001  per  share,  of SIGA
TECHNOLOGIES,  INC. and tenders herewith payment in accordance with Section 1 of
said Common Stock Purchase Warrant.

         Please deliver the stock certificate to:




Dated:___________________________




[Name of Holder]



By:


[ ]     CASH:                              $____________________




                                                                       Exhibit G

      THESE SECURITIES INCLUDING ANY UNDERLYING SECURITIES (THE "SECURITIES")
      HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
      THE SECURITIES LAWS OF ANY STATE AND MAY NOT BE SOLD OR OFFERED FOR SALE
      IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES
      OR AN OPINION OF COUNSEL OR OTHER EVIDENCE ACCEPTABLE TO THE COMPANY THAT
      SUCH REGISTRATION IS NOT REQUIRED.

                            SIGA, TECHNOLOGIES, INC.

                          COMMON STOCK PURCHASE WARRANT

         1. Issuance; Certain Definitions. In consideration of good and valuable
consideration,  the receipt of which is hereby acknowledged by SIGA TECHNOLOGIES
INC., a Delaware  corporation (the "Company"),  GABRIEL M. CERRONE or registered
assigns (the  "Holder") is hereby granted the right to purchase at any time from
the  Commencement  Date (defined  below) until 5:00 P.M., New York City time, on
March 28, 2005 (the "Expiration Date"), Three Hundred Three Thousand Two Hundred
(303,200) fully paid and nonassessable  shares of the Company's Stock, par value
$.0001 per share (the  "Common  Stock") at an initial  exercise  price per share
(the "Exercise Price") of $5.00 per share,  subject to further adjustment as set
forth herein.  Reference is made to that certain Securities  Purchase Agreement,
dated as of January 31, 2000 (the "Securities Purchase Agreement"), to which the
Company and certain  named Buyers are parties.  Capitalized  terms not otherwise
defined  herein  shall  have the  meanings  ascribed  to them in the  Securities
Purchase Agreement.

         2. Exercise of Warrants.

            2.1 General.  This Warrant is exercisable in whole or in part at any
time and from time to time.  Such exercise shall be effectuated by submitting to
the Company  (either by delivery to the Company or by facsimile  transmission as
provided in Section 8 hereof) a completed and duly  executed  Notice of Exercise
(substantially in the form attached to this Warrant  Certificate) as provided in
this  paragraph.  The date such Notice of Exercise is faxed to the Company shall
be the "Exercise  Date,"  provided that the Holder of this Warrant  tenders this
Warrant Certificate to the Company within five (5) business days thereafter. The
Notice of Exercise  shall be  executed  by the Holder of this  Warrant and shall
indicate the number of shares then being  purchased  pursuant to such  exercise.
Upon  surrender of this Warrant  Certificate  with,  together  with  appropriate
payment of the  Exercise  Price for the shares of Common  Stock  purchased,  the
Holder shall be entitled to receive a certificate or certificates for the shares
of Common Stock so purchased.  The Exercise  Price per share of Common Stock for
the shares  then being  exercised  shall be payable in cash or by  certified  or
official  bank check.  The Holder shall be deemed to be the holder of the shares
issuable to it in  accordance  with the  provisions  of this  Section 2.1 on the
Exercise Date.

            2.2 Limitation on Exercise.  Notwithstanding  the provisions of this
Warrant, in no event (except (i) as specifically  provided in this Warrant as an
exception to this  provision,  or (ii) while there is outstanding a tender offer
for any or all of the shares of the



Company's  Common  Stock) shall the Holder be entitled to exercise this Warrant,
or shall the  Company  have  either the  obligation  to issue  shares  upon such
exercise of all or any portion of this Warrant,  to the extent that,  after such
exercise the sum of (1) the number of shares of Common Stock  beneficially owned
by the Holder and its affiliates (other than shares of Common Stock which may be
deemed  beneficially  owned through the ownership of the unexercised  portion of
the  Warrants),  and (2) the number of shares of Common Stock  issuable upon the
exercise of the Warrants with respect to which the determination of this proviso
is being  made,  would  result in  beneficial  ownership  by the  Holder and its
affiliates of more than 9.99% of the  outstanding  shares of Common Stock (after
taking into  account the shares to be issued to the Holder upon such  exercise).
For purposes of the proviso to the immediately  preceding  sentence,  beneficial
ownership  shall  be  determined  in  accordance  with  Section  1.3(d)  of  the
Securities  Exchange  Act of 1934,  as  amended  (the  "1934  Act"),  except  as
otherwise provided in clause (1) of such sentence. The Holder, by its acceptance
of this Warrant,  further agrees that if the Holder  transfers or assigns any of
the Warrants to a party who or which would not be considered  such an affiliate,
such assignment shall be made subject to the transferee's or assignee's specific
agreement  to be  bound  by the  provisions  of  this  Section  2.2  as if  such
transferee or assignee were the original Holder hereof.

            2.3 Commencement Date. The term "Commencement  Date" means March 28,
2000.

         3.  Reservation of Shares.  The Company hereby agrees that at all times
during the term of this  Warrant  there  shall be  reserved  for  issuance  upon
exercise of this  Warrant  such number of shares of its Common Stock as shall be
required for issuance upon exercise of this Warrant (the "Warrant Shares").

         4.  Mutilation  or Loss of  Warrant.  Upon  receipt  by the  Company of
evidence  satisfactory  to it of the loss,  theft,  destruction or mutilation of
this  Warrant,  and (in the  case of  loss,  theft or  destruction)  receipt  of
reasonably  satisfactory  indemnification,  and (in the case of mutilation) upon
surrender and cancellation of this Warrant, the Company will execute and deliver
a new  Warrant of like tenor and date and any such lost,  stolen,  destroyed  or
mutilated Warrant shall thereupon become void.

         5. Rights of the Holder.  The Holder  shall not, by virtue  hereof,  be
entitled to any rights of a stockholder in the Company, either at law or equity,
and the rights of the Holder and limited to those  expressed in this Warrant and
are not enforceable against the Company except to the extent set forth herein.

         6. Protection Against Dilution.

            6.1 Adjustment Mechanism.  If an adjustment of the Exercise Price is
required  pursuant to this  Section 6, the Holder  shall be entitled to purchase
such  number of  additional  shares of Common  Stock as will cause (i) the total
number of shares of Common Stock Holder is entitled to purchase pursuant to this
Warrant,  multiplied  by (ii) the adjusted  Exercise  Price per share,  to equal
(iii) the dollar  amount of the total number of shares of Common Stock Holder is
entitled to purchase  before  adjustment  multiplied by the total Exercise Price
before adjustment.

                                      -2-



            6.2 Capital Adjustments. In case of any stock split or reverse stock
split, stock dividend,  reclassification of the Common Stock,  recapitalization,
merger or consolidation,  or like capital adjustment  affecting the Common Stock
of the  Company,  the  provisions  of this Section 6 shall be applied as if such
capital  adjustment  event had  occurred  immediately  prior to the date of this
Warrant and the original  Exercise Price had been fairly  allocated to the stock
resulting from such capital adjustment;  and in other respects the provisions of
this Section shall be applied in a fair,  equitable and reasonable  manner so as
to give effect,  as nearly as may be, to the purposes  hereof. A rights offering
to  stockholders  shall be deemed a stock  dividend to the extent of the bargain
purchase element of the rights.

            6.3  Adjustment  for Spin  Off.  If,  for any  reason,  prior to the
exercise of this Warrant in full,  the Company  spins off or  otherwise  divests
itself of a part of its business or  operations  or disposes all or of a part of
its assets in a  transaction  (the  "Spin  Off") in which the  Company  does not
receive  compensation  for such  business,  operations  or  assets,  but  causes
securities  of  another  entity  (the  "Spin  Off  Securities")  to be issued to
security holders of the Company, then

           (a) the Company  shall cause (i) to be reserved  Spin Off  Securities
      equal to the number thereof which would have been issued to the Holder had
      all of the Holder's  unexercised  Warrants  outstanding on the record date
      (the  "Record  Date")  for  determining  the amount and number of Spin Off
      Securities  to  be  issued  to  security   holders  of  the  Company  (the
      "Outstanding  Warrants") been exercised as of the close of business on the
      trading day  immediately  before the Record Date (the  "Reserved  Spin Off
      Shares"),  and (ii) to be issued to the Holder on the  exercise  of all or
      any of the  Outstanding  Warrants,  such amount of the  Reserved  Spin Off
      Shares  equal to (x) the  Reserved  Spin Off  Shares  multiplied  by (y) a
      fraction,  of which (I) the  numerator  is the  amount of the  Outstanding
      Warrants then being  exercised,  and (II) the denominator is the amount of
      the Outstanding Warrants; and

           (b) the Exercise Price on the Outstanding  Warrants shall be adjusted
      immediately after consummation of the Spin Off by multiplying the Exercise
      Price by a fraction (if, but only if, such fraction is less than 1.0), the
      numerator  of which is the Average  Market  Price of the Common  Stock (as
      defined  below) for the five (5) trading days  immediately  following  the
      fifth trading day after the Record Date,  and the  denominator of which is
      the Average  Market Price of the Common Stock on the five (5) trading days
      immediately  preceding the Record Date;  and such adjusted  Exercise Price
      shall be deemed to be the Exercise  Price with respect to the  Outstanding
      Warrants after the Record Date. As used herein,  the term "Average  Market
      Price of the Common Stock" means the average  closing bid price of a share
      of Common Stock, as reported by Bloomberg,  LP or, if not so reported,  as
      reported on the over-the-counter market for the relevant period.

         7. Transfer to Comply with the Securities Act; Registration Rights.

            7.1  Transfer.  This  Warrant  has not  been  registered  under  the
Securities  Act of 1933,  as  amended,  (the  "Act") and has been  issued to the
Holder  for  investment  and not with a view to the  distribution  of either the
Warrant or the  Warrant  Shares.  Neither  this

                                      -3-



Warrant nor any of the Warrant Shares or any other  security  issued or issuable
upon exercise of this Warrant may be sold, transferred,  pledged or hypothecated
in the absence of an effective  registration statement under the Act relating to
such  security  or an  opinion  of  counsel  satisfactory  to the  Company  that
registration  is not required under the Act. Each  certificate  for the Warrant,
the Warrant  Shares and any other  security  issued or issuable upon exercise of
this Warrant shall  contain a legend on the face thereof,  in form and substance
satisfactory  to counsel for the  Company,  setting  forth the  restrictions  on
transfer contained in this Section.

            7.2  Registration   Rights.   (a)  The  Company  agrees  to  file  a
registration statement or an amendment to its registration statement on Form S-3
to  register  all of the  Warrant  Shares  (as so  filed  or  amended,  the "New
Registration  Statement"),  pursuant to the  Securities Act of 1933, as amended,
and to have such New Registration  Statement at no cost or expense to the Holder
(other than any costs or  commissions  which would be borne by the Holder  under
the terms of the Registration Rights Agreement were the Warrant Shares deemed to
be Registrable  Securities  under that  agreement).  The Company  further agrees
that,  after the New  Registration  Statement  is  declared  effective,  it will
thereafter  maintain the effectiveness of such registration until the earlier of
the date on which both (i) the Holder has exercised  all of the Holder's  rights
to acquire Warrant Shares or the Warrant has expired,  whichever is earlier, and
(ii) the Holder has sold or  otherwise  transferred  all of the  Warrant  Shares
acquired upon exercise of this warrant.

           (b)  In  addition  to  the  registration  rights  referred  to in the
      preceding provisions of Section 7.2(a),  effective after the expiration of
      the effectiveness of the New Registration Statement as contemplated by the
      Registration   Rights   Agreement,   the  Holder  shall  have   piggy-back
      registration  rights with  respect to the Warrant  Shares then held by the
      Holder  or  then  subject  to  issuance  upon  exercise  of  this  Warrant
      (collectively,  the "Remaining Warrant Shares),  subject to the conditions
      set forth below. If, at any time after the New Registration  Statement has
      ceased to be effective,  the Company participates  (whether voluntarily or
      by reason of an  obligation to a third party) in the  registration  of any
      shares of the Company's  stock (other than a  registration  on Form S-4 on
      form S-8), the Company shall give written notice thereof to the Holder and
      the Holder shall have the right, exercisable within ten (10) business days
      after receipt of such notice,  to demand  inclusion of all or a portion of
      the Holder's Remaining Warrant Shares in such registration  statement.  If
      the Holder  exercises  such  election,  the  Remaining  Warrant  Shares so
      designated shall be included in the  registration  statement at no cost or
      expense to the Holder (other than any costs or commissions  which would be
      borne by the Holder under the terms of the  Registration  Rights Agreement
      were the Warrant  Shares deemed to be  Registrable  Securities  under that
      agreement).

           (c) The  Holder's  rights  under this  Section 7 shall expire at such
      time as the Holder  can sell all of the  Warrant  Shares  then held by the
      Holder and all shares  then  subject to  issuance  upon  exercise  of this
      Warrant under Rule 144 without volume or other restrictions or limit.

         8.  Notices.  Any notice or other  communication  required or permitted
hereunder  shall be in writing and shall be delivered  personally,  telegraphed,
telexed,  sent by facsimile  transmission  or sent by  certified,  registered or
express mail,  postage  pre-paid.  Any

                                      -4-



such notice  shall be deemed given when so  delivered  personally,  telegraphed,
telexed or sent by  facsimile  transmission,  or, if mailed,  two days after the
date of deposit in the United States mails, as follows:

                  (i)   if to the Company, to;

                        Siga Technologies, Inc.
                        420 Lexington Avenue, Suite 620
                        New York, New York 10170
                        Attn:  Judson Cooper
                        Telephone No.:  (212) 672-9150
                        Telecopier No.:  (212) 697-3130

                        and with a copy to:

                        Orrick Herrington & Sutcliffe, LLP
                        666 Fifth Avenue
                        New York, NY 10103
                        Attn:  Jeffrey Fessler, Esq.
                        Telephone No.:  (212) 506-5000
                        Telecopier No.:  (212) 506-5151

                  (ii)  if to the Holder, to:

                        Gabriel M. Cerrone
                        265 E. 66th St.
                        Apt. 16G
                        New York, NY 10021

                        Telephone No.: (212) 755-6003
                        Telecopier No.: (212) 755-6574

                        with a copy to:

                        Krieger & Prager LLP, Esqs.
                        39 Broadway
                        Suite 1440
                        New York, NY 10006
                        Attn: Samuel Krieger, Esq.
                        Telephone No.: (212) 363-2900
                        Telecopier No.: (212) 363-2999

            Any party may be notice given in accordance with this Section to the
other parties designate another address or person for receipt of notices
hereunder.

         9.  Supplements and Amendments;  Whole  Agreement.  This Warrant may be
amended or  supplemented  only by an instrument in writing signed by the parties
hereto. This

                                      -5-



Warrant of even date  herewith  contain  the full  understanding  of the parties
hereto with  respect to the subject  matter  hereof and thereof and there are no
representations,  warranties,  agreements or understandings other than expressly
contained herein and therein.

         10.  Governing  Law. This Warrant shall be deemed to be a contract made
under the laws of the State of New York for contracts to be wholly  performed in
such state and without  giving effect to the  principles  thereof  regarding the
conflict  of laws.  Each of the  parties  consents  to the  jurisdiction  of the
federal courts whose districts encompass any part of the City of New York or the
state  courts  of the  State  of New  York  sitting  in the  City of New York in
connection with any dispute arising under this Warrant and hereby waives, to the
maximum extent permitted by law, any objection, including any objection based on
forum  non  conveniens,   to  the  bringing  of  any  such  proceeding  in  such
jurisdictions.  To the  extent  determined  by such  court,  the  Company  shall
reimburse the Holder for any reasonable legal fees and disbursements incurred by
the Buyer in  enforcement of or protection of any of its rights under any of the
Transaction Agreements.

         11.  Counterparts.  This  Warrant  may be  executed  in any  number  of
counterparts and each of such  counterparts  shall for all purposes be deemed to
be an original,  and all such counterparts shall together constitute but one and
the same instrument.

         12. Descriptive Headings.  Descriptive headings of the several Sections
of this  Warrant  are  inserted  for  convenience  only and shall not control or
affect the meaning or construction of any of the provisions hereof.

         IN WITNESS WHEREOF, the parties hereto have executed this Warrant as of
the 1st day of May, 2000.

                                    SIGA TECHNOLOGIES, INC.



                                    By:
                                        --------------------------------------
                                        Name:  Joshua D. Schein
                                        Title: Chief Executive Officer


                                      -6-



                          NOTICE OF EXERCISE OF WARRANT

            The undersigned hereby irrevocably elects to exercise the right,
represented by the Warrant Certificate dated as of , , to purchase shares of the
Common Stock, par value $0001 per share, of SIGA TECHNOLOGIES, INC. and tenders
herewith payment in accordance with Section 1 of said Common Stock Purchase
Warrant.

            Please deliver the stock certificate to:




Dated: ___________________________



[Name of Holder]



By:


[ ]      CASH:                               $_____________________




                                                                       Exhibit H

                          REGISTRATION RIGHTS AGREEMENT

      THIS REGISTRATION RIGHTS AGREEMENT, dated as of January __, 2000, is made
by and between SIGA PHARMACEUTICALS, INC., a Delaware corporation, with
headquarters located at 420 Lexington Avenue, Suite 620, New York , New York
10170 (the "Company") and each entity named on a signature page hereto (each, an
"Initial Investor") (each agreement with an Initial Investor being deemed a
separate and independent agreement between the Company and such Initial
Investor, except that each Initial Investor acknowledges and consents to the
rights granted to each other Initial Investor under such agreement).

      Terms not otherwise defined herein shall have the meanings ascribed to
them in the Securities Purchase Agreement, dated as of January __, 2000 (the
"Securities Purchase Agreement"), between the Initial Investor and the Company.

                              W I T N E S S E T H:

            WHEREAS, upon the terms and subject to the conditions of the
Securities Purchase Agreement, the Company has agreed to issue and sell to the
Initial Investor the Company's 6% Convertible Debentures having an aggregate
principal balance of up to $1,500,000 (the "Debentures"); and

            WHEREAS, the Company has agreed to issue Warrants to the Initial
Investor as contemplated by the Securities Purchase Agreement (the "Warrants");
and

            WHEREAS, the Debentures are convertible into shares of Common Stock
(the "Conversion Shares"; which term, for purposes of this Agreement, shall
include shares of Common Stock of the Company issuable in lieu of accrued
interest on conversion as contemplated by the Debentures and as Reset Shares as
contemplated by the Securities Purchase Agreement) upon the terms and subject to
the conditions contained in the Debentures and the Securities Purchase
Agreement, and the Warrants may be exercised for the purchase of shares of
Common Stock (the "Warrant Shares") upon the terms and conditions of the
Warrants; and

            WHEREAS, to induce the Initial Investor to execute and deliver the
Securities Purchase Agreement, the Company has agreed to provide certain
registration rights under the Securities Act of 1933, as amended, and the rules
and regulations thereunder, or any similar successor statute (collectively, the
"Securities Act"), with respect to the Conversion Shares and the Warrant Shares;

            NOW, THEREFORE, in consideration of the premises and the mutual
covenants contained herein and other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the Company and the
Initial Investor hereby agree as follows:



            1. Definitions. As used in this Agreement, the following terms shall
have the following meanings:

            (a)  "Investor"   means  the  Initial  Investor  and  any  permitted
transferee  or assignee  who agrees to become  bound by the  provisions  of this
Agreement in accordance with Section 9 hereof and who holds Debentures, Warrants
or Registrable Securities.

            (b) "Potential  Material Event" means any of the following:  (i) the
possession by the Company of material  information  not ripe for disclosure in a
registration statement, which shall be evidenced by determinations in good faith
by the Board of Directors of the Company that disclosure of such  information in
the  registration  statement would be detrimental to the business and affairs of
the Company;  or (ii) any material  engagement  or activity by the Company which
would, in the good faith determination of the Board of Directors of the Company,
be adversely  affected by disclosure in a  registration  statement at such time,
which  determination  shall be accompanied by a good faith  determination by the
Board of  Directors  of the Company  that the  registration  statement  would be
materially misleading absent the inclusion of such information.

            (c)  "Register,"   "Registered,"  and  "Registration"   refer  to  a
registration  effected  by  preparing  and filing a  Registration  Statement  or
Statements in compliance  with the Securities Act and pursuant to Rule 415 under
the Securities Act or any successor rule providing for offering  securities on a
continuous  basis ("Rule 415"), and the declaration or ordering of effectiveness
of such  Registration  Statement by the United  States  Securities  and Exchange
Commission (the "SEC").

            (d)  "Registrable  Securities"  means the Conversion  Shares and the
Warrant  Shares.  Notwithstanding  the  above:  (1)  Common  Stock  which  would
otherwise  be  deemed  to  be  Registrable   Securities   shall  not  constitute
Registrable Securities if those shares of Common Stock may be resold in a public
transaction  without volume or other limitations and without  registration under
the Act, including, without limitation,  pursuant to Rule 144 under the Act; and
(2) any Registrable  Securities  resold in a public  transaction  shall cease to
constitute Registrable Securities.

            (e) "Registration  Statement" means a registration  statement of the
Company under the Securities Act.

            (f) "Required  Effective Date" means the relevant  Initial  Required
Effective Date or Increased  Required Effective Date (as those terms are defined
below).

            2. Registration.

            (a) Mandatory Registration.

                (i)     The Company shall prepare and file with the SEC, as soon
                        as  possible  after the  Closing  Date but no later than
                        thirty (30) days after the Closing  Date (the  "Required
                        Filing Date"),  either a Registration  Statement on Form
                        S-3  or  an  amendment   to  an  existing   Registration
                        Statement, in either event registering for resale by the
                        Investor  the number of shares  equal to one hundred ten
                        percent (110%) of the sum of (A) the Purchase Price plus

                                      -2-



                        accrued interest on the Debentures  through the Maturity
                        Date of the Debentures, divided by the Conversion Price,
                        plus (B) the number of Warrant  Shares,  or such  lesser
                        number as may be required by the SEC.  The  Registration
                        Statement  (X)  shall   include  only  the   Registrable
                        Securities  and the  shares  referred  to in  Exhibit  1
                        annexed  hereto;  and (Y)  shall  also  state  that,  in
                        accordance  with Rule 416 and 457  under the  Securities
                        Act,  it  also  covers  such  indeterminate   number  of
                        additional shares of Common Stock as may become issuable
                        upon  conversion of the  Debentures  and the exercise of
                        the Warrants to prevent  dilution  resulting  from stock
                        splits,  or stock  dividends.  The Company  will use its
                        reasonable  best  efforts  to  cause  such  Registration
                        Statement  to  be  declared  effective  on a  date  (the
                        "Initial  Required  Effective Date") which no later than
                        is the earlier of (Y) five (5) days after  notice by the
                        SEC that it may be declared effective or (Z) ninety (90)
                        days after the Closing Date.

                (ii)    If at any time,  the  number  of shares of Common  Stock
                        represented by the Registrable  Shares,  issued or to be
                        issued as contemplated  by the  Transaction  Agreements,
                        exceeds the  aggregate  number of shares of Common Stock
                        then registered (an "Increased Registered Shares Date"),
                        the Company  shall,  within ten (10) business days after
                        receipt of a written  notice from any  Investor,  either
                        (V)  amend  the  Registration  Statement  filed  by  the
                        Company  pursuant to the  preceding  provisions  of this
                        Section 2, if such  Registration  Statement has not been
                        declared  effective by the SEC at that time, to register
                        such Registrable  Shares,  computed,  (1)with respect to
                        Shares  previously  issued,  as  the  number  of  shares
                        actually issued,  and (W) with respect to Shares not yet
                        issued,  utilizing the Conversion  Price, or (X) if such
                        Registration  Statement has been  declared  effective by
                        the SEC at that  time,  file with the SEC an  additional
                        Registration  Statement on Form S-3 or other appropriate
                        registration statement form (an "Additional Registration
                        Statement")  to  register  the  shares of  Common  Stock
                        represented  by  the  Registrable  Shares,  computed  as
                        contemplated by the immediately  preceding  subparagraph
                        (i),  that  exceed  the  aggregate  number  of shares of
                        Common Stock  already  registered.  The Company will use
                        its reasonable  best efforts to cause such  Registration
                        Statement to be declared  effective on a date (each,  an
                        "Increased  Required  Effective Date") which is no later
                        than (Q) with respect to a Registration  Statement under
                        clause  (V)  of  this  subparagraph  (ii),  the  Initial
                        Required  Effective  Date  and (R)  with  respect  to an
                        Additional  Registration  Statement,  the earlier of (I)
                        five (5)  days  after  notice  by the SEC that it may be
                        declared  effective  or (II)  thirty (30) days after the
                        Increased Registered Shares Date.

            (b) Payments by the Company.

                (i)     If the Registration  Statement  covering the Registrable
Securities  is not filed with the SEC by the Required  Filing Date in the proper
form  required by this  Agreement,  the Company will make payment to the Initial
Investor in such  amounts and at such times as shall be  determined  pursuant to
this Section 2(b).

                (ii)    If the Registration  Statement  covering the Registrable
Securities is not effective by the relevant  Required  Effective  Date or if the
Investor is restricted from making sales of Registrable  Securities covered by a
previously  effective   Registration  Statement  at  any  time  (the  date  such
restriction  commences, a "Restricted Sale Date") after the Effective Date other
than during a Permitted  Suspension Period (as defined below),  then the Company
will make payments to the Initial  Investor in such amounts and at such times as
shall be determined pursuant to this Section 2(b).

                                      -3-



                (iii)   The amount  (the  "Periodic  Amount")  to be paid by the
Company to the Initial  Investor shall be determined as of each Computation Date
(as  defined  below)  and such  amount  shall be  equal to the  Periodic  Amount
Percentage  (as defined  below) of the  principal  for all the  Debentures  (the
"Debenture  Principal")  for the period  from the date  following  the  relevant
Required  Filing Date,  Required  Effective Date or Restricted Sale Date, as the
case may be, to the first  relevant  Computation  Date,  and  thereafter to each
subsequent  Computation  Date. The "Periodic  Amount  Percentage"  means (A) two
percent (2%) of the Debenture  Principal for all  Debentures for the period from
the date following the relevant Required Filing Date, Required Effective Date or
Restricted  Sale  Date,  as the case may be, to the first  relevant  Computation
Date, and (B) three percent (3%) of such  Debenture  Principal of all Debentures
to each  Computation Date  thereafter.  Anything in the preceding  provisions of
this paragraph (iii) to the contrary  notwithstanding,  after the Effective Date
the Debenture Principal shall be deemed to refer to the sum of (X) the principal
of all  Debentures  not yet  converted  and (Y) the Held  Debentures  Value  (as
defined below).  The "Held  Debentures  Value" means, for shares acquired by the
Investor upon a conversion  within the thirty (30) days preceding the Restricted
Sale Date,  but not yet sold by the Investor,  the  principal of the  Debentures
converted into such Conversion Shares;  provided,  however, that if the Investor
effected  more than one  conversion  during such thirty (30) day period and sold
less than all of such  shares,  the sold  shares  shall be deemed to be  derived
first from the  conversions  in the sequence of such  conversions  (that is, for
example, until the number of shares from the first of such conversions have been
sold,  all shares shall be deemed to be from the first  conversion;  thereafter,
from  the  second  conversion  until  all  such  shares  are  sold).  By  way of
illustration  and  not in  limitation  of  the  foregoing,  if the  Registration
Statement  is  timely  filed but is not  declared  effective  until one  hundred
sixty-five  (165) days after the Initial  Closing Date, the Periodic Amount will
aggregate  eight  percent (8%) of the  Debenture  Principal (2% for days 91-120,
plus 3% for days 121-150, plus 3% for days 151-165).

                (iv)    Each  Periodic  Amount will be payable by the Company in
cash or other  immediately  available  funds to the  Investor  monthly,  without
requiring demand therefor by the Investor.

                (v)     The parties  acknowledge  that the damages  which may be
incurred  by the  Investor  if the  Registration  Statement  is not filed by the
Required  Filing Date or if the  Registration  Statement  has not been  declared
effective  by a  Required  Effective  Date,  including  if  the  right  to  sell
Registrable  Securities under a previously effective  Registration  Statement is
suspended,  may be difficult to  ascertain.  The parties agree that the Periodic
Amounts  represent a reasonable  estimate on the part of the parties,  as of the
date of this Agreement, of the amount of such damages.

                (vi)    Notwithstanding  the foregoing,  the amounts  payable by
the Company  pursuant to this  provision  shall not be payable to the extent any
delay in the  effectiveness of the  Registration  Statement occurs because of an
act of, or a failure  to act or to act  timely by the  Initial  Investor  or its
counsel, or in the event all of the Registrable  Securities may be sold pursuant
to Rule 144 or another available exemption under the Act.

                (vii)   "Computation  Date"  means  (A) the  date  which  is the
earlier of (1) thirty (30) days after the  Required  Filing  Date,  any relevant
Required  Effective  Date or a

                                      -4-



Restricted  Sale Date,  as the case may be, or (2) the date  after the  Required
Filing Date,  such Required  Effective Date or Restricted Sale Date on which the
Registration Statement is filed (with respect to payments due as contemplated by
Section 2(b)(i) hereof) or is declared effective or has its restrictions removed
(with respect to payments due as contemplated by Section  2(b)(ii)  hereof),  as
the case may be, and (B) each date which is the  earlier of (1) thirty (30) days
after  the  previous  Computation  Date  or (2)  the  date  after  the  previous
Computation Date on which the  Registration  Statement is filed (with respect to
payments due as contemplated by Section 2(b)(i) hereof) or is declared effective
or has its restrictions removed (with respect to payments due as contemplated by
Section 2(b)(ii) hereof), as the case may be.

                (viii)  Anything in the  preceding  provisions  of this  Section
2(b)  to the  contrary  notwithstanding,  if,  but  only  if,  the  Registration
Statement is declared  effective  within one hundred twenty (120) days following
the Initial Closing Date, the provisions of Section  2(b)(ii) shall not apply to
the fact that the Registration  Statement was initially declared effective after
the  Initial  Required  Effective  Date,  and the  Company  will  not  have  any
obligation  to pay any  Periodic  Amount to the Initial  Investor  with  respect
thereto;  provided,  however,  that the  provisions  of Section  2(b)(ii)  shall
continue to apply to all other events described therein.

            3.  Obligations of the Company.  In connection with the registration
of the Registrable Securities, the Company shall do each of the following.

            (a) Prepare  promptly,  and file with the SEC by the Required Filing
Date a  Registration  Statement  with  respect  to not less  than the  number of
Registrable  Securities  provided in Section 2(a) above,  and thereafter use its
reasonable  best  efforts  to cause  such  Registration  Statement  relating  to
Registrable  Securities to become  effective by the Required  Effective Date and
keep the  Registration  Statement  effective at all times during the period (the
"Registration Period") continuing until the earliest of (i) the date that is two
(2) years after the last day of the calendar month  following the month in which
the  Effective  Date  occurs,  (ii) the date  when  the  Investors  may sell all
Registrable  Securities  under Rule 144 without volume or other  restrictions or
limits or (iii) the date the  Investors  no  longer  own any of the  Registrable
Securities,   which   Registration   Statement   (including  any  amendments  or
supplements  thereto and prospectuses  contained  therein) shall not contain any
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements  therein,  in light of the
circumstances in which they were made, not misleading;

            (b)  Prepare  and  file  with  the SEC  such  amendments  (including
post-effective amendments) and supplements to the Registration Statement and the
prospectus  used  in  connection  with  the  Registration  Statement  as  may be
necessary to keep the Registration  Statement  effective at all times during the
Registration  Period,  and,  during the  Registration  Period,  comply  with the
provisions  of  the  Securities  Act  with  respect  to the  disposition  of all
Registrable  Securities  of the Company  covered by the  Registration  Statement
until such time as all of such  Registrable  Securities have been disposed of in
accordance  with the intended  methods of  disposition  by the seller or sellers
thereof as set forth in the Registration Statement;

            (c)  Permit a  single  firm of  counsel  designated  by the  Initial
Investors  to  review  the   Registration   Statement  and  all  amendments  and
supplements  thereto a  reasonable

                                      -5-



period of time (but not less than three (3) business days) prior to their filing
with  the  SEC,  and not  file any  document  in a form to  which  such  counsel
reasonably objects.

            (d) Notify each Investor,  such Investor's legal counsel  identified
to the Company  (which,  until further  notice,  shall be deemed to be Krieger &
Prager LLP, ATTN: Samuel Krieger, Esq.; each, an "Investor's Counsel"),  and any
managing  underwriters  immediately  (and, in the case of (i)(A) below, not less
than five (5) days prior to such  filing) and (if  requested by any such Person)
confirm such notice in writing no later than one (1) business day  following the
day (i)(A) when a Prospectus  or any  Prospectus  supplement  or  post-effective
amendment to the  Registration  Statement is proposed to be filed;  (B) whenever
the  SEC  notifies  the  Company  whether  there  will  be a  "review"  of  such
Registration  Statement;  (C) whenever the Company receives (or a representative
of the Company receives on its behalf) any oral or written comments from the SEC
in respect of a Registration Statement (copies or, in the case of oral comments,
summaries  of such  comments  shall be promptly  furnished by the Company to the
Investors);   and  (D)  with  respect  to  the  Registration  Statement  or  any
post-effective  amendment,  when  the  same has  become  effective;  (ii) of any
request by the SEC or any other  Federal  or state  governmental  authority  for
amendments or  supplements  to the  Registration  Statement or Prospectus or for
additional  information;  (iii) of the  issuance  by the SEC of any  stop  order
suspending the effectiveness of the Registration  Statement  covering any or all
of the  Registrable  Securities or the  initiation of any  proceedings  for that
purpose;  (iv) if at any time any of the  representations  or  warranties of the
Company  contained  in any  agreement  (including  any  underwriting  agreement)
contemplated hereby ceases to be true and correct in all material respects;  (v)
of the receipt by the Company of any notification with respect to the suspension
of the  qualification or exemption from  qualification of any of the Registrable
Securities for sale in any jurisdiction, or the initiation or threatening of any
proceeding for such purpose; and (vi) of the occurrence of any event that to the
best  knowledge  of the Company  makes any  statement  made in the  Registration
Statement  or  Prospectus  or  any  document   incorporated   or  deemed  to  be
incorporated  therein  by  reference  untrue  in any  material  respect  or that
requires  any  revisions  to the  Registration  Statement,  Prospectus  or other
documents so that, in the case of the Registration  Statement or the Prospectus,
as the case may be, it will not contain any untrue  statement of a material fact
or omit to state any material fact required to be stated therein or necessary to
make the statements therein, in light of the circumstances under which they were
made, not misleading,  unless such material change, untrue statement or omission
is not  properly  and  timely  disclosed  in a  document  incorporated  into the
Registration Statement or Prospectus.

            (e)  Furnish  to each  Investor  and  such  Investor's  Counsel  (i)
promptly  after the same is prepared  and publicly  distributed,  filed with the
SEC, or received by the  Company,  one (1) copy of the  Registration  Statement,
each  preliminary  prospectus and  prospectus,  and each amendment or supplement
thereto, and (ii) such number of copies of a prospectus,  and all amendments and
supplements  thereto and such other  documents,  as such Investor may reasonably
request in order to facilitate  the  disposition of the  Registrable  Securities
owned by such Investor;

            (f) As promptly as practicable after becoming aware thereof,  notify
each Investor of the happening of any event of which the Company has  knowledge,
as a result of which the prospectus included in the Registration  Statement,  as
then in effect,  includes  an untrue  statement  of a material  fact or omits to
state a material  fact  required to be stated  therein or

                                      -6-



necessary to make the statements  therein,  in light of the circumstances  under
which they were made,  not  misleading,  and use its best  efforts  promptly  to
prepare  a  supplement  or  amendment  to the  Registration  Statement  or other
appropriate  filing with the SEC to correct  such untrue  statement or omission,
and deliver a number of copies of such  supplement or amendment to each Investor
as such Investor may reasonably request;

            (g) As promptly as practicable after becoming aware thereof,  notify
each Investor who holds  Registrable  Securities being sold (or, in the event of
an underwritten  offering, the managing underwriters) of the issuance by the SEC
of a Notice of Effectiveness or any notice of effectiveness or any stop order or
other  suspension  of the  effectiveness  of the  Registration  Statement at the
earliest possible time;

            (h)  Notwithstanding  the foregoing,  if at any time or from time to
time after the date of effectiveness of the Registration Statement,  the Company
notifies  the  Investors  in writing of the  existence  of a Potential  Material
Event,  the Investors  shall not offer or sell any  Registrable  Securities,  or
engage  in any  other  transaction  involving  or  relating  to the  Registrable
Securities,  from the time of the giving of notice  with  respect to a Potential
Material Event until such Investor receives written notice from the Company that
such  Potential  Material  Event  either has been  disclosed to the public or no
longer  constitutes a Potential  Material  Event;  provided,  however,  that the
Company may not so suspend the right to such holders of  Registrable  Securities
during the periods the Registration  Statement is required to be in effect other
than  during a  Permitted  Suspension  Period.  The term  "Permitted  Suspension
Period" means one or more  suspension  periods during any  consecutive  12-month
period which  suspension  periods,  in the  aggregate,  do not exceed fifty (50)
days, provided,  however, that no one such suspension period shall either (i) be
for more than  twenty (20) days or (ii) begin less than ten (10)  business  days
after the last day of the preceding suspension (whether or not such last day was
during or after a Permitted Suspension Period).

            (i)  Use  its   reasonable   efforts  to  secure  and  maintain  the
designation  of all  the  Registrable  Securities  covered  by the  Registration
Statement on the "OTC SmallCap Market" of the National Association of Securities
Dealers  Automated  Quotations  System ("NASDAQ") within the meaning of Rule I 1
Aa2-1 of the SEC under the  Securities  Exchange  Act of 1934,  as amended  (the
"Exchange Act"),  and the quotation of the Registrable  Securities on The NASDAQ
Bulletin Board Market; and, without limiting the generality of the foregoing, to
arrange for at least two market makers to register with the National Association
of Securities  Dealers,  Inc.  ("NASD") as such with respect to such Registrable
Securities;

            (j) Provide a transfer  agent and  registrar,  which may be a single
entity, for the Registrable  Securities not later than the effective date of the
Registration Statement;

            (k)  Cooperate   with  the   Investors  to  facilitate   the  timely
preparation  and delivery of certificates  for the Registrable  Securities to be
offered pursuant to the Registration  Statement and enable such certificates for
the Registrable  Securities to be in such  denominations  or amounts as the case
may be, as the Investors may reasonably request,  and, within three (3) business
days after a Registration  Statement  which includes  Registrable  Securities is
ordered  effective by the SEC, the Company shall deliver,  and shall cause legal
counsel  selected  by the  Company to  deliver,  to the  transfer  agent for the
Registrable   Securities  (with  copies  to  the

                                      -7-



Investors  whose  Registrable  Securities  are  included  in  such  Registration
Statement) an appropriate instruction and opinion of such counsel; and

            (l) Take all other  reasonable  actions  necessary  to expedite  and
facilitate disposition by the Investor of the Registrable Securities pursuant to
the Registration Statement.

            4. Obligations of the Investors. In connection with the registration
of  the  Registrable   Securities,   the  Investors  shall  have  the  following
obligations:

            (a) It shall be a  condition  precedent  to the  obligations  of the
Company to complete the registration  pursuant to this Agreement with respect to
the  Registrable  Securities of a particular  Investor that such Investor  shall
furnish to the  Company  such  information  regarding  itself,  the  Registrable
Securities held by it, and the intended method of disposition of the Registrable
Securities  held  by  it,  as  shall  be  reasonably   required  to  effect  the
registration of such Registrable  Securities and shall execute such documents in
connection  with such  registration  as the Company may reasonably  request.  At
least  ten  (10)  days  prior  to  the  first  anticipated  filing  date  of the
Registration   Statement,   the  Company  shall  notify  each  Investor  of  the
information  the  Company  requires  from each  such  Investor  (the  "Requested
Information") if such Investor elects to have any of such Investor's Registrable
Securities included in the Registration  Statement. If at least two (2) business
days  prior to the  filing  date the  Company  has not  received  the  Requested
Information from an Investor (a "Non-Responsive Investor"), then the Company may
file the Registration Statement without including Registrable Securities of such
Non-Responsive Investor;

            (b) Each Investor,  by such Investor's acceptance of the Registrable
Securities,  agrees to cooperate with the Company as reasonably requested by the
Company  in  connection  with the  preparation  and  filing of the  Registration
Statement hereunder, unless such Investor has notified the Company in writing of
such  Investor's  election  to  exclude  all  of  such  Investor's   Registrable
Securities from the Registration Statement; and

            (c) Each Investor  agrees that,  upon receipt of any notice from the
Company of the  happening of any event of the kind  described in Section 3(e) or
3(f),  above,  such  Investor  will  immediately   discontinue   disposition  of
Registrable  Securities  pursuant to the  Registration  Statement  covering such
Registrable  Securities  and will not  engage in any other  transactions  in the
Company's  securities  until  such  Investor's  receipt  of  the  copies  of the
supplemented or amended prospectus  contemplated by Section 3(e) or 3(f) and, if
so directed by the Company,  such Investor  shall deliver to the Company (at the
expense of the Company) or destroy (and deliver to the Company a certificate  of
destruction)  all  copies  in  such  Investor's  possession,  of the  prospectus
covering  such  Registrable  Securities  current  at the time of receipt of such
notice.  Each  Investor  also  agrees to  maintain  the  confidentiality  of the
information  in  such  notice   referred  to  in  the  first  sentence  of  this
subparagraph (c).

            5. Expenses of Registration. (a) All reasonable expenses (other than
underwriting  discounts and commissions of the Investor)  incurred in connection
with  registrations,  filings  or  qualifications  pursuant  to  Section  3, but
including,  without limitation,  all registration,  listing,  and qualifications
fees,  printers and accounting  fees, the fees and  disbursements of counsel for
the  Company  shall be borne by the  Company.  In  addition,  a fee for

                                      -8-



a single counsel to review the Registration Statement on behalf of the Investors
equal to, in the  aggregate  for all  Investors,  $3,500,  shall be borne by the
Company.

            (b) Neither the Company nor any of its  subsidiaries  has, as of the
date hereof, nor shall the Company nor any of its subsidiaries,  on or after the
date of this Agreement,  enter into any agreement with respect to its securities
that is inconsistent  with the rights granted to the Investors in this Agreement
or otherwise  conflicts with the provisions hereof.  Neither the Company nor any
of its  subsidiaries  has  previously  entered into any  agreement  granting any
registration  rights with respect to any of its  securities  to any Person other
than Open-i.  Without  limiting the  generality  of the  foregoing,  without the
written  consent  of  the  Investors  holding  a  majority  of  the  Registrable
Securities,  the Company  shall not grant to any person the right to request the
Company to register  any  securities  of the Company  under the  Securities  Act
unless the rights so granted are subject in all  respects to the prior rights in
full of the  Investors  set forth  herein,  and are not otherwise in conflict or
inconsistent  with the  provisions of this  Agreement and the other  Transaction
Agreements.

            6.  Indemnification.  In the event any  Registrable  Securities  are
included in a Registration Statement under this Agreement:

            (a) To the extent  permitted by law, the Company will  indemnify and
hold  harmless  each  Investor  who  holds  such  Registrable  Securities,   the
directors,  if any, of such  Investor,  the officers,  if any, of such Investor,
each  person,  if any,  who  controls  any  Investor  within the  meaning of the
Securities  Act  or  the  Exchange  Act  (each,  an   "Indemnified   Person"  or
"Indemnified  Party"),  against  any losses,  claims,  damages,  liabilities  or
expenses (joint or several)  incurred  (collectively,  "Claims") to which any of
them may become subject under the Securities Act, the Exchange Act or otherwise,
insofar  as such  Claims  (or  actions  or  proceedings,  whether  commenced  or
threatened,  in  respect  thereof)  arise  out of or are  based  upon any of the
following statements,  omissions or violations in the Registration Statement, or
any post-effective  amendment thereof, or any prospectus  included therein:  (i)
any untrue statement or alleged untrue statement of a material fact contained in
the  Registration  Statement  or any  post-effective  amendment  thereof  or the
omission or alleged  omission to state  therein a material  fact  required to be
stated therein or necessary to make the statements therein not misleading,  (ii)
any untrue statement or alleged untrue statement of a material fact contained in
the final  prospectus  (as amended or  supplemented,  if the  Company  files any
amendment thereof or supplement thereto with the SEC) or the omission or alleged
omission to state  therein any material  fact  necessary to make the  statements
made therein,  in light of the circumstances  under which the statements therein
were made,  not  misleading or (iii) any  violation or alleged  violation by the
Company of the Securities Act, the Exchange Act, any state securities law or any
rule or  regulation  under the  Securities  Act,  the  Exchange Act or any state
securities  law (the matters in the  foregoing  clauses (i) through (iii) being,
collectively,  "Violations").  Subject  to  clause  (b) of this  Section  6, the
Company shall  reimburse the  Investors,  promptly as such expenses are incurred
and  are due and  payable,  for any  legal  fees or  other  reasonable  expenses
incurred by them in connection with  investigating  or defending any such Claim.
Notwithstanding  anything to the contrary contained herein, the  indemnification
agreement  contained in this Section 6(a) shall not (I) apply to a Claim arising
out of or based upon a Violation which occurs in reliance upon and in conformity
with  information  furnished  in writing  to the  Company by or on behalf of any
Indemnified  Person  expressly for use in connection with the preparation of the
Registration  Statement or any such

                                      -9-



amendment  thereof or supplement  thereto,  if such  prospectus  was timely made
available by the Company  pursuant to Section 3(c) hereof;  (II) be available to
the extent such Claim is based on a failure of the  Investor to deliver or cause
to be delivered the  prospectus  (or the  amendment or supplement  thereto) made
available by the  Company;  (III) be available to the extent such Claim is based
on a breach of the  Investor's  breach of Section 4(c) hereof;  or (IV) apply to
amounts paid in settlement of any Claim if such  settlement is effected  without
the  prior  written  consent  of  the  Company,   which  consent  shall  not  be
unreasonably  withheld.  Each  Investor  will  indemnify  the  Company  and  its
officers,  directors and agents (each, an  "Indemnified  Person" or "Indemnified
Party") against any claims arising out of or based upon a Violation which occurs
in reliance upon and in conformity with information  furnished in writing to the
Company, by or on behalf of such Investor,  expressly for use in connection with
the  preparation  of the  Registration  Statement or the amendment or supplement
thereto,  subject to such  limitations  and  conditions as are applicable to the
Indemnification  provided by the Company to this Section 6. Such indemnity shall
remain in full force and effect  regardless of any  investigation  made by or on
behalf  of  the  Indemnified  Person  and  shall  survive  the  transfer  of the
Registrable Securities by the Investors pursuant to Section 9.

            (b) Promptly after receipt by an  Indemnified  Person or Indemnified
Party  under  this  Section  6 of  notice  of the  commencement  of  any  action
(including any  governmental  action),  such  Indemnified  Person or Indemnified
Party  shall,  if a  Claim  in  respect  thereof  is  to  be  made  against  any
indemnifying  party under this  Section 6, deliver to the  indemnifying  party a
written notice of the commencement thereof and the indemnifying party shall have
the right to  participate  in,  and,  to the  extent the  indemnifying  party so
desires,  jointly with any other indemnifying party similarly noticed, to assume
control  of the  defense  thereof  with  counsel  mutually  satisfactory  to the
indemnifying  party and the Indemnified  Person or the Indemnified Party, as the
case maybe. In case any such action is brought against any Indemnified Person or
Indemnified  Party, and it notifies the  indemnifying  party of the commencement
thereof,  the indemnifying party will be entitled to participate in, and, to the
extent that it may wish,  jointly with any other  indemnifying  party  similarly
notified,  assume the defense thereof,  subject to the provisions  herein stated
and after  notice  from the  indemnifying  party to such  Indemnified  Person or
Indemnified  Party  of its  election  so to  assume  the  defense  thereof,  the
indemnifying  party will not be liable to such Indemnified Person or Indemnified
Party  under  this  Section  6 for any legal or other  reasonable  out-of-pocket
expenses  subsequently  incurred by such Indemnified Person or Indemnified Party
in  connection  with  the  defense  thereof  other  than  reasonable   costs  of
investigation,  unless the indemnifying party shall not pursue the action of its
final  conclusion.  The Indemnified  Person or Indemnified  Party shall have the
right to employ  separate  counsel in any such action and to  participate in the
defense  thereof,  but the fees and  reasonable  out-of-pocket  expenses of such
counsel  shall  not  be  at  the  expense  of  the  indemnifying  party  if  the
indemnifying party has assumed the defense of the action with counsel reasonably
satisfactory  to the  Indemnified  Person or Indemnified  Party.  The failure to
deliver written notice to the indemnifying party within a reasonable time of the
commencement of any such action shall not relieve such indemnifying party of any
liability to the Indemnified  Person or Indemnified  Party under this Section 6,
except to the extent that the indemnifying party is prejudiced in its ability to
defend such action. The indemnification required by this Section 6 shall be made
by  periodic   payments  of  the  amount   thereof  during  the  course  of  the
investigation or defense, as such expense, loss, damage or liability is incurred
and is due and payable.

                                      -10-



            7.   Contribution.   To  the  extent  any   indemnification   by  an
indemnifying  party is  prohibited  or limited by law,  the  indemnifying  party
agrees to make the maximum contribution with respect to any amounts for which it
would  otherwise be liable under  Section 6 to the fullest  extent  permitted by
law;  provided,   however,   that  (a)  no  contribution  shall  be  made  under
circumstances  where the maker  would not have been  liable for  indemnification
under the fault  standards set forth in Section 6; (b) no seller of  Registrable
Securities guilty of fraudulent misrepresentation (within the meaning of Section
11 (f) of the Securities Act) shall be entitled to contribution  from any seller
of   Registrable   Securities   who  was   not   guilty   of   such   fraudulent
misrepresentation;  and (c) contribution by any seller of Registrable Securities
shall be limited in amount to the net amount of proceeds received by such seller
from the sale of such Registrable Securities.

            8. Reports under  Exchange  Act. With a view to making  available to
the Investors the benefits of Rule 144  promulgated  under the Securities Act or
any other  similar rule or regulation of the SEC that may at any time permit the
Investors to sell  securities of the Company to the public without  registration
("Rule 144"), the Company agrees to:

            (a) file  with the SEC in a timely  manner  all  reports  and  other
documents required of the Company under the Securities Act and the Exchange Act,
or,  if the  provisions  of Rule  144(c)(2)  are  applicable,  ensure  that  the
standards  contemplated  by Rule 144(c) to permit sales by the  Investors  under
said Rule 144 are satisfied at all times; and

            (b)  furnish  to  each  Investor  so  long  as  such  Investor  owns
Registrable  Securities,  promptly upon request,  (i) a written statement by the
Company that it has complied  with the reporting  requirements  of Rule 144, the
Securities  Act and the Exchange  Act,  (ii) a copy of the most recent annual or
quarterly report of the Company and such other reports and documents so filed by
the Company and (iii) such other  information as may be reasonably  requested to
permit  the  Investors  to sell such  securities  pursuant  to Rule 144  without
registration.

            9.  Assignment of the  Registration  Rights.  The rights to have the
Company  register  Registrable  Securities  pursuant to this Agreement  shall be
automatically  assigned by the Investors to any  transferee  of the  Registrable
Securities (or all or any portion of any  unconverted  Debentures or unexercised
Warrant)  only if: (a) the  Investor  agrees in writing with the  transferee  or
assignee to assign such rights, and a copy of such agreement is furnished to the
Company  within a  reasonable  time after such  assignment,  (b) the Company is,
within a  reasonable  time after such  transfer or  assignment,  furnished  with
written  notice of (i) the name and address of such  transferee  or assignee and
(ii) the  securities  with respect to which such  registration  rights are being
transferred or assigned,  (c) immediately  following such transfer or assignment
the further  disposition  of such  securities  by the  transferee or assignee is
restricted  under the Securities Act and applicable  state  securities laws, and
(d) at or before the time the Company  received the written notice  contemplated
by clause (b) of this sentence the transferee or assignee agrees in writing with
the Company to be bound by all of the provisions  contained herein. In the event
of any delay in filing  or  effectiveness  of the  Registration  Statement  as a
result of such  assignment,  the  Company  shall not be liable  for any  damages
arising  from such  delay,  or the  payments  set forth in Section  2(b)  hereof
arising from such delay.

                                      -11-



            10.  Amendment  of  Registration   Rights.  Any  provision  of  this
Agreement  may be  amended  and the  observance  thereof  may be waived  (either
generally   or  in  a   particular   instance   and  either   retroactively   or
prospectively),  only with the written  consent of the Company and Investors who
hold a sixty-seven  (67%) percent  interest of the Registrable  Securities.  Any
amendment or waiver effected in accordance with this Section 10 shall be binding
upon each Investor and the Company.

            11.  Termination.  This  Agreement  shall  terminate on the date all
Registrable Securities cease to exist; but without prejudice to (i) the parties'
rights and obligations  arising from breaches of this Agreement  occurring prior
to such  termination  and (ii)  other  indemnification  obligations  under  this
Agreement.

            12. Miscellaneous.

            (a) Notices  required or  permitted to be given  hereunder  shall be
given in the manner contemplated by the Securities Purchase Agreement, (i) if to
the Company or to the Initial Investor, to their respective address contemplated
by the Securities  Purchase  Agreement,  and (iii) if to any other Investor,  at
such address as such Investor shall have provided in writing to the Company,  or
at such other address as each such party furnishes by notice given in accordance
with this Section 12(a).

            (b) Failure of any party to exercise  any right or remedy under this
Agreement or otherwise,  or delay by a party in exercising such right or remedy,
shall not operate as a waiver thereof.

            (c)  This  Agreement   shall  be  governed  by  and  interpreted  in
accordance  with the laws of the State of Delaware  for  contracts  to be wholly
performed  in such state and without  giving  effect to the  principles  thereof
regarding the conflict of laws. Each of the parties consents to the jurisdiction
of the  federal  courts  whose  districts  encompass  any  part  of the  City of
Wilmington  or the state courts of the State of Delaware  sitting in the City of
Wilmington  in  connection  with any dispute  arising  under this  Agreement and
hereby waives, to the maximum extent permitted by law, any objection,  including
any  objection  based  on  forum  non  coveniens,  to the  bringing  of any such
proceeding in such  jurisdictions.  To the extent  determined by such court, the
Company  shall  reimburse  the  Investor  for  any  reasonable  legal  fees  and
disbursements incurred by the Investor in enforcement of or protection of any of
its rights under this Agreement.

            (d)  If  any  provision  of  this  Agreement  shall  be  invalid  or
unenforceable in any jurisdiction, such invalidity or unenforceability shall not
affect the validity or  enforceability of the remainder of this Agreement or the
validity or enforceability of this Agreement in any other jurisdiction.

            (e) Subject to the requirements of Section 9 hereof,  this Agreement
shall inure to the benefit of and be binding upon the  successors and assigns of
each of the parties hereto.

            (f) All pronouns and any variations  thereof refer to the masculine,
feminine or neuter, singular or plural, as the context may require.

                                      -12-



            (g) The headings in this Agreement are for  convenience of reference
only and shall not limit or otherwise affect the meaning thereof.

            (h) This Agreement may be executed in one or more counterparts, each
of which shall be deemed an original but all of which shall  constitute  one and
the same agreement.  This Agreement,  once executed by a party, may be delivered
to the other party hereto by telephone line facsimile  transmission of a copy of
this Agreement bearing the signature of the party so delivering this Agreement.

            (i) This  Agreement  constitutes  the  entire  agreement  among  the
parties  hereto  with  respect  to  the  subject  matter  hereof.  There  are no
restrictions,  promises, warranties or undertakings,  other than those set forth
or  referred to herein.  This  Agreement  supersedes  all prior  agreements  and
understandings  among the  parties  hereto with  respect to the  subject  matter
hereof. This Agreement may be amended only by an instrument in writing signed by
the party to be charged with enforcement thereof.

            (j)  Fahnestock  & Co.,  Inc.  and  Krieger  & Prager  LLP and their
respective  designees  with respect to the  securities  referred to in Exhibit I
shall be deemed third-party beneficiaries of Section 2(a).

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]



                                      -13-




      IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed by their respective officers thereunto duly authorized as of the day
and year first above written.

                                    COMPANY:
                                    SIGA PHARMACEUTICALS, INC.



                                    By: /s/ Judson Cooper
                                        --------------------------------
                                    Name:  Judson Cooper
                                    Title:  Chairman


                                    INITIAL INVESTOR:

                                    Donald G. Drapkin
                                    ------------------------------------



                                    By:  /s/ Donald G.Drapkin
                                         -------------------------------
                                    Name:  Donald G. Drapkin
                                    Title:________________________________



                                      -14-



                                                                       Exhibit I


                                Donald G. Drapkin
                               35 East 62nd Street
                            New York, New York 10021

                                 March 30, 2001


SIGA Technologies, Inc.
420 Lexington Avenue, Suite 620
New York, New York 10170

Gabriel M. Cerrone
265 East 66th Street, Suite 16G
New York, New York  10021

Thomas E. Constance
c/o Kramer Levin Naftalis & Frankel LLP
919 Third Avenue
New York, New York  10022

Eric A. Rose, M.D.
112 East 78th Street
New York, New York  10021

Judson A. Cooper
c/o SIGA Technologies, Inc.
420 Lexington Avenue, Suite 620
New York, New York  10170

Joshua D. Schein, Ph.D.
c/o SIGA Technologies, Inc.
420 Lexington Avenue, Suite 620
New York, New York  10170

      Re:   SIGA Technologies, Inc. ("SIGA").
            --------------------------------

Gentlemen:

            This  letter is to confirm  the  understanding  (the  "Agreement")
among Donald G. Drapkin  ("Drapkin"),  SIGA,  Gabriel M. Cerrone  ("Cerrone"),
Thomas E. Constance  ("Constance"),  Eric A. Rose,  M.D.  ("Rose"),  Judson A.
Cooper  ("Cooper") and Joshua D. Schein,  Ph.D.  ("Schein" and,  together with
Drapkin,  SIGA,  Cerrone,  Constance,  Rose and Cooper,  the "Parties"),  with
respect to certain matters relating to SIGA.

      1.  Resignations.  On or before  April 16,  2001 or such  other date as is
consented to by Drapkin (the "Effective Date"),  each of Cooper and Schein shall
(i) resign from the Board of  Directors  of SIGA (the  "Board") and from any and
all  offices  held with SIGA and (ii) use his best

                                       1



efforts to cause each of the Resigning  Directors  (as defined  below) to resign
from  the  Board  and from  any and all  offices  held  with  SIGA by each  such
Resigning Director, in each case, at no cost to SIGA. "Resigning Director" shall
mean each member of the Board other than Schein and Cooper;  provided,  however,
that the "Resigning  Directors" shall not be construed to include Drapkin or any
of his designees.

      2.  Appointments.  Cooper and Schein shall use their best efforts to cause
Drapkin and his designees to be elected to the Board.

      3. Termination of Employment  Agreements.  (a) On the Effective Date, each
of Cooper and Schein shall cause any agreement or other arrangement  relating to
their  respective  employment  by  SIGA,  including,   without  limitation,  the
respective Amended and Restated  Employment  Agreements between SIGA and each of
Cooper and Schein,  dated as of October 6, 2000,  to be  immediately  terminated
voluntarily  and at no cost  to  SIGA,  pursuant  to the  respective  Separation
Agreement  between  each  such  Party  and  SIGA  of  even  date  herewith  (the
"Separation  Agreements"),  other  than  costs  expressly  provided  for in this
Agreement.

            (b) At Drapkin's request, on or after the Effective Date, each of
Cooper and Schein shall cause any consulting agreements or other arrangements
between SIGA and any entity controlled by Cooper or Schein, including, without
limitation, Prism Ventures LLC, to be immediately terminated at no cost to SIGA.

            (c) On the Effective Date, SIGA shall enter into Mutual Releases
with each of Cooper and Schein and with each Resigning Director, in the form
attached hereto as Exhibit A.

      4.  Cooperation.  (a) From the period commencing on the Effective Date and
terminating on the first  anniversary  thereof,  each of Cooper and Schein shall
cooperate  with  SIGA,  if and as  reasonably  requested  by SIGA,  to  effect a
transition  of  their  respective  responsibilities  and to  ensure  that  their
respective successors and SIGA are aware of all matters that had been handled by
such Party. Such cooperation by each of Cooper and Schein shall include, without
limitation,  performing up to ten hours per month of consulting services to SIGA
if and as reasonably  requested by SIGA.  After  receiving an invoice  therefor,
SIGA shall pay such  Party  $175 per hour  consulting  work  actually  performed
pursuant  to, and within the scope of, a request for such  services  made by the
Chief Executive Officer of SIGA.

            (b) Following the Effective Date, each of Cooper and Schein shall,
upon reasonable notice, furnish such information and assistance to SIGA as may
reasonably be required by SIGA in connection with any legal action, suit,
proceeding, claim, complaint, dispute or investigation, whether at law, in
equity, in arbitration or before the government of any nation, state, city,
locality or other political subdivision thereof or any entity exercising
executive, legislative, judicial, regulatory or administrative functions of or
pertaining to government, and including any external or internal investigation,
involving SIGA or any of its affiliates or in which any of them is, or may
become, a party.

      5. Books and Records.  On the  Effective  Date,  each of Cooper and Schein
shall turn over,  and shall  cause  SIGA to turn over,  to Drapkin or  Drapkin's
designee, all books and records of SIGA.

                                       2



      6.  Lock-Up.  (a) Each of Cooper and Schein shall not, and shall cause its
respective  affiliates to not,  directly or  indirectly,  offer,  sell,  pledge,
hypothecate,  contract to sell,  acquire any option to sell, grant any option to
purchase,  short or otherwise dispose of (or announce any offer, sale,  contract
of sale or other disposition of) (collectively,  "Transfer") any shares acquired
either  prior to April 16, 2001 or pursuant to grants or vesting of either stock
options or restricted stock thereafter, or any interest acquired either prior to
April 16,  2001 or  pursuant  to grants or  vesting of either  stock  options or
restricted stock thereafter in any shares, of common stock, par value $.0001 per
share  ("Common  Stock"),  other capital stock of SIGA or any  Convertibles  (as
defined  below),  during the period  commencing on the date hereof and ending on
April 16,  2003 (the  "Lock-Up  Period"),  except that each of Cooper and Schein
shall,  notwithstanding the above restrictions,  be entitled to Transfer (i) any
such securities pursuant to a pledge or hypothecation to the extent necessary to
margin them in a brokerage account (a "Permitted  Pledge"),  (ii) 250,000 in the
case of Schein,  or 220,500 in the case of Cooper,  shares of Common Stock on or
after October 16, 2001 and (iii) an additional 125,000 shares of Common Stock on
or after each of April 16, 2002, July 16, 2002, October 16, 2002 and January 16,
2003;  provided that, in any event, such Party shall not Transfer in any one day
more than the greater of (x) 10,000  shares of Common  Stock and (y) a number of
shares of Common Stock equal to 5% of the total volume of shares of Common Stock
traded on the open  market on such day.  Notwithstanding  Cooper's  relationship
with his  children,  they  shall  not be  deemed an  "affiliate"  of Cooper  for
purposes of this Agreement.

            (b) Subject to the conditions contained in Section 13 hereof, Each
of Drapkin, Cerrone, Constance and Rose shall not, and shall cause its
respective affiliates to not Transfer any shares acquired either prior to April
16, 2001 or pursuant to grants or vesting of either stock options or restricted
stock thereafter, or any interest acquired either prior to April 16, 2001 or
pursuant to grants or vesting of either stock options or restricted stock
thereafter in any shares, of Common Stock, other capital stock of SIGA or any
Convertibles, during the Lock-Up Period, except that each of Drapkin, Cerrone,
Constance and Rose shall, notwithstanding the above restrictions, be entitled to
Transfer (i) any such securities pursuant to a Permitted Pledge, (ii) on or
after October 16, 2001, 24.2% of the securities "beneficially owned" (as defined
below) by such person as of October 16, 2001 which remain subject to such
restrictions, (iii) on or after April 16, 2002, 16.0% of the securities
beneficially owned by such person as of April 16, 2002 which remain subject to
such restrictions, (iv) on or after July 16, 2002, 19.0% of the securities
beneficially owned by such person as of July 16, 2002 which remain subject to
such restrictions, (v) on or after October 16, 2002, 23.5% of the securities
beneficially owned by such person as of October 16, 2002 which remain subject to
such restrictions and (vi) on or after January 16, 2003, 30.7% of the securities
beneficially owned by such person as of January 16, 2003 which remain subject to
such restrictions; provided that, in any event, such Party shall not Transfer in
any one day more than the greater of (x) 10,000 shares of Common Stock and (y) a
number of shares of Common Stock equal to 5% of the total volume of shares of
Common Stock traded on the open market on such day. As used in this Agreement,
the term beneficially ownership shall have the meaning ascribed to it in Rule
13d-3 promulgated under the Securities Exchange Act of 1934, as amended, except
that, for purposes hereof: (A) all Common Stock issuable upon conversion or
exercise of Convertibles shall be deemed "beneficially owned," notwithstanding
any limitation on the conversion or exercise thereof based on the amount of
securities beneficially owned by the holder thereof; and (B) the 11,750 shares
of Common Stock owned by the Drapkin Family Charity Foundation (the "Charity")
shall not be deemed beneficially owned by Drapkin. Furthermore,

                                       3



notwithstanding  Drapkin's  relationship with the Charity, the Charity shall not
be deemed an "affiliate" of Drapkin for purposes of this Agreement.

            (c) At any time or times, at Drapkin's option, the provisions of
Subsections 6(a) and 6(b) (the "Lock-Up") may be (i) terminated as a whole and
rendered null and void; or (ii) modified so that the number of shares of Common
Stock that each Party is allowed to Transfer shall be increased, pro rata in
accordance with their respective beneficial ownership of Common Stock, by such
amount as Drapkin shall decide in his sole discretion. Any such termination or
modification of the Lock-Up shall be effective on and after the date specified
in a notice from Drapkin to each other Party, which notice is sent no fewer than
five days prior to such termination or modification of the Lock-Up. In the case
of any modification of the Lock-Up in accordance with clause (ii) of the first
sentence of this Subsection 6(c), Drapkin shall state the amount of such
modification in the notice thereof required by the immediately preceding
sentence.

            (d) If a Party or an affiliate of such Party consummates any
Transfer in violation of Subsection 6(a) or 6(b), such Party shall immediately
pay to SIGA an amount of liquidated damages equal to the gross sales price of
such securities or interest.

            (e) No Party shall hold any shares of Common Stock, Convertibles or
other capital stock of SIGA through any broker that has not agreed to send
copies of all confirmations with respect to such securities to SIGA. SIGA shall
keep records of all such confirmations received, and each Party shall have the
right, upon at least five days prior written notice to SIGA, to inspect such
records during SIGA's regular business hours, at SIGA's offices, at such
inspecting Party's expense; provided, however, that no Party may exercise such
inspection right more than once in any period of 90 consecutive calendar days.
Upon at least ten days prior written notice from any Party (in such capacity the
"Inspector") to any Party other than SIGA (in such capacity the "Inspected"),
the Inspected shall provide the Inspector with copies of the Inspected's two
most recent monthly statements for each of such Inspected's securities accounts
that contains Common Stock, Convertibles or other capital stock of SIGA, which
copies may be redacted so long as the information relating to holdings of, and
transactions in, any such SIGA securities subject to the Lock-Up are visible;
provided, however, that no Inspector may exercise such inspection right more
than once in any period of 180 consecutive calendar days with respect to the
same Inspected. No Party shall give SIGA's transfer agent stop transfer
instructions solely on account of the Lock-Up; provided that such stop transfer
instructions may be given with respect to any shares held by a Party that has
breached this Section 6, including without limitation, any shares held in
violation of the first sentence of this Subsection 6(e). The provisions of this
Subsection 6(e) shall terminate 90 days after the end of the Lock-Up Period.

            (f) On the Effective Date, Cooper and Schein shall grant to Drapkin
an irrevocable proxy for the duration of the Lock-Up Period, in substantially
the form attached hereto as Exhibit B, with respect to all shares of capital
stock of SIGA held by such Party.

      7.  Representations  and  Warranties.  Each of Cooper  and  Schein  hereby
represents  and warrants,  as of the date hereof and as of the  Effective  Date,
each of the following:

            (a) Since December 15, 2000, SIGA has taken no action for which
approval of the Board was required nor has the Board approved any action, except
for (i) the execution and

                                       4



delivery of and performance  under this Agreement and (ii) filing a Registration
Statement on Form S-8  registering  Common Stock issued in  connection  with the
Plan (as defined below), which actions have been duly authorized by the Board.

            (b) Since December 15, 2000, no options or other rights to purchase
securities of SIGA have vested or otherwise become exercisable nor have the
provisions of any such options or other rights been amended or modified, except
(i) the vesting pursuant to the original terms thereof of options to purchase
Common Stock held by each of Thomas Konatich and David Kaufman, to the extent of
12,500 shares each, (ii) the vesting pursuant to the original terms thereof of
options to purchase 25,000 shares of Common Stock held by Dennis Hruby and (iii)
as expressly provided in this Agreement.

            (c)   SIGA  has  no  contingent   liabilities  (whether  known  or
unknown).

            (d) Except as set forth on Schedule 7(d) hereto, SIGA is neither
contemplating, nor is obligated to engage in, any transaction or transactions
whereby SIGA would pay or receive compensation (in any form) that could
reasonably be valued at $5,000 or more individually or $20,000 or more in the
aggregate. Except for transactions pursuant to Sections 8 and 9 of this
Agreement, as of the date hereof and as of the Effective Date, SIGA has not and
will not have consummated, nor does or will SIGA have any binding obligation
with respect to, is SIGA or will SIGA be obligated to incur any cost for failing
to consummate, any transaction described on Schedule 7(d).

            (e) Except as set forth on Schedule 7(e) hereto, there are no: (i)
outstanding options, warrants or other rights to acquire Common Stock; (ii)
securities convertible into or exchangeable for Common Stock; nor (iii) any
rights (contingent or otherwise) to acquire, directly or indirectly, any of (i)
or (ii), above ((i), (ii) and (iii), above, are referred to collectively as
"Convertibles"). Schedule 7(e) sets forth, for each Convertible, all vesting and
expiration dates and the number of shares of Common Stock subject thereto.

            (f) Except as set forth on Schedule 7(f), no spouse or child of
either Cooper or Schein owns any Common Stock, Convertibles or other securities
of SIGA.

            (g) Neither Cooper nor Schein beneficially owns any Common Stock,
Convertibles or other securities of SIGA except as set forth on Schedule 7(g).

            (h) Except as set forth on Schedule 7(h), SIGA is not party to any
agreements or other arrangements or any amendments, renewals or other
modifications thereof relating to the employment by SIGA of any person other
than Cooper and Schein.

            (i) The exercise price applicable to the Unvested Options (as
defined below) is $1.125 per share of Common Stock. The Expiring Options (as
defined below) were issued in three equal tranches, and the respective exercise
prices applicable to each tranche of the Expiring Options are $1.50, $5.00 and
$4.00 per share of Common Stock.

            (j) Other than the Common Stock, SIGA does not have any other
classes of voting securities outstanding.

                                       5



            (k) Except as expressly provided in this Agreement or disclosed in
SIGA's public filings under the Securities Exchange Act of 1934, as amended, up
to and including SIGA's proxy statement filed September 28, 2000, as of the date
hereof and as of the Effective Date, none of the terms of any of the Resigning
Directors' stock options, restricted stock or other awards, whether granted
under the Plan or otherwise, have been modified, nor have any agreements or
arrangements been entered into to so modify them.

            (l) The modifications to the terms of the Unvested Options and the
Expiring Options pursuant to Section 8 hereof is permissible under the Plan.

The representations and warranties contained in this Section 7 shall survive
until April 16, 2003.

      8. Adjustments to Certain Options. Subject to the conditions of Section 13
hereof:  (i) SIGA shall  cause any  employee  stock  options  held by Cooper and
Schein that are  scheduled to vest on November 1, 2001, to the extent of options
to purchase up to 37,500 shares of Common Stock each (the  "Unvested  Options"),
to instead vest on the  Effective  Date;  and (ii) SIGA shall cause any employee
stock  options held by Cooper and Schein,  that would  expire  within 90 days of
such  Party's  termination,  to the extent of options to  purchase  up to 50,001
shares of Common  Stock each (the  "Expiring  Options"),  to remain  exercisable
until such options would otherwise expire in accordance with their terms.

      9. Fees of  Counsel.  SIGA shall pay for Cooper  and  Schein's  reasonable
attorneys' fees and disbursements,  of no more than $20,000 in the aggregate, in
connection with this Agreement upon an accounting  therefor.  SIGA shall pay for
Drapkin's  reasonable  attorneys' fees and disbursements in connection with this
Agreement upon an accounting therefor.

      10.  Mutual  Release.  (a)  Drapkin,  on behalf of himself and each of his
predecessors,  successors, heirs, executors,  administrators,  assigns ("Drapkin
Releasor")  hereby  releases,  remises  and forever  discharges  each of Cooper,
Schein and the members of the current Board of Directors of SIGA,  together with
each and all of their respective  predecessors,  successors,  heirs,  executors,
administrators,  assigns  ("Drapkin  Releasees")  from the  Released  Claims (as
defined below).  "Released Claims" means all actions,  causes of action,  suits,
debts,  dues,  sums of money,  accounts,  controversies,  agreements,  promises,
variances,  trespasses,  damages,  judgments,  abstracts  of  judgments,  liens,
extents, executions,  claims and demands whatsoever, in law, admiralty or equity
(collectively, "Claims"), which the Releasor ever had, now has or hereafter can,
shall or may have against any or all of the Releasees, for, upon or by reason of
any matter,  cause or thing whatsoever regarding SIGA or Drapkin's investment in
SIGA from the  beginning of the world to the day of the date of this  Agreement,
except for (i) Claims  arising  out of or  related  to this  Agreement  and (ii)
Claims  arising  out of or  resulting  from  any  Drapkin  Releasee's  fraud  or
intentional  misconduct.  Drapkin Releasor  further  covenants and agrees not to
bring suit against the Drapkin Releasees for any Released Claims.

            (b) Each of Cooper and Schein, on behalf of themselves, each other
and the members of the current Board of Directors of SIGA, in each case together
with each and all of their respective predecessors, successors, heirs,
executors, administrators, assigns (collectively, the "Insider Releasors")
hereby releases, remises and forever discharges Drapkin, together with each and
all of his predecessors, successors, heirs, executors, administrators and
assigns ("Insider

                                       6



Releasees")  from all Claims  which any Insider  Releasor  ever had,  now has or
hereafter  can,  shall or may have against any or all of the Insider  Releasees,
for, upon or by reason of any matter,  cause or thing whatsoever  regarding SIGA
or Drapkin's  investment  in SIGA from the  beginning of the world to the day of
the date of this  Agreement,  except for (i) Claims arising out of or related to
this  Agreement  and (ii) Claims  arising out of or  resulting  from any Insider
Releasee's  fraud or  intentional  misconduct.  Each  Insider  Releasor  further
covenants  and agrees not to bring suit  against any Insider  Releasees  for any
Released Claims.

      11. Registration.  Subject to any suspension or black-out periods that are
applicable  generally  to  SIGA's  securities  that  are  registered  under  the
Securities Act of 1933, as amended (the  "Securities  Act"),  SIGA shall use its
best efforts to have its Registration  Statement on Form S-8 registering  Common
Stock  issued in  connection  with SIGA's  employee  stock  incentive  plan (the
"Plan") remain effective with respect to each option issued to Cooper and Schein
under the Plan until the earlier of (i) the later of (A) the date of  expiration
of such  option and (B) the one year  anniversary  of the last date on which any
portion of such option is actually  exercised and (ii) the one year  anniversary
of the date on which such  option or any  remaining  portion of such  option has
been  exercised  in full.  If SIGA fails to comply with the  provisions  of this
Section 11, lost profits  sustained by Cooper or Schein shall be deemed ordinary
damages, to the extent proven to be caused by SIGA's breach of this Section 11.

      12. Insurance and Indemnification. Except as otherwise provided herein:

            (a) SIGA shall use its best efforts to provide each of Cooper and
Schein with the same health insurance benefits that SIGA currently provides such
Party until the earlier of (i) such Party's obtaining employment by an entity
other than SIGA and (ii) April 16, 2003.

            (b) SIGA shall use its best efforts to maintain Directors and
Officers insurance at least as protective as its current policy.

            (c) SIGA shall indemnify, in accordance with and to the full extent
permitted by law, Cooper, Schein and any Resigning Director (each an
"Indemnified Party") that is a party or is threatened to be made a party to any
pending or threatened action, suit or proceeding, whether civil, criminal,
administrative or investigative, by reason of Indemnified Party's acting as a
director of SIGA, against any liability or expense actually and reasonably
incurred by such Indemnified Party in respect thereof; provided, however, that,
SIGA shall not be obligated to indemnify any such Indemnified Party (i) with
respect to proceedings, claims or actions initiated or brought voluntarily by
such Indemnified Party and not by way of defense, (ii) for any amounts paid in
settlement of an action effected without the prior written consent of SIGA to
such settlement or (iii) with respect to proceedings, claims or actions based
upon or attributable to such Indemnified Party gaining in fact a personal profit
or advantage to which such Indemnified Party is not entitled, (iv) with respect
to proceedings, claims or actions resulting from such Indemnified Party's gross
negligence or willful misconduct or (v) with respect to proceedings, claims or
actions, the indemnification in respect of which by SIGA is not permitted by
applicable law ((i) through (v) are collectively referred to herein as the
"Indemnification Exclusions").

            (d) If any Indemnified Party receives notice with respect to any
matter that may give rise to a claim for indemnification under Subsection 12(c),
then such Indemnified Party shall

                                       7



promptly  thereafter  (and in any event  within ten days of receipt of notice of
such matter)  notify SIGA,  describing  the nature of the claim and stating that
indemnification may be sought with respect to such matter. The Indemnified Party
shall  cooperate  with SIGA to  familiarize  SIGA with the  nature of the claim,
including  providing  copies of all  information  and materials  relating to the
claim.  SIGA shall be  entitled  to assume  the  defense of any matter for which
indemnification  is  sought  in  accordance  with  Subsection  12(c);  provided,
however,  that SIGA  shall pay the  reasonable  fees and  expenses  of  separate
counsel retained by the Indemnified Party if SIGA's counsel  determines,  in its
sole  discretion,  that there is a conflict of interest.  In the event that SIGA
does not assume the defense of the matter,  then the Indemnified  Party shall be
entitled to defend  against  the matter;  provided  that the  assumption  of the
defense of the matter by the Indemnified  Party shall not prejudice the right of
SIGA to later  assume the defense of the matter (and as long as such  assumption
would not  reasonably  be  expected  to have a  material  adverse  impact on the
conduct of the defense of the matter). In the event that SIGA incurs expenses of
any kind  (including,  without  limitation,  legal  fees and  disbursements)  in
defending,  or in reimbursing the defense of, any Indemnified  Party from, or in
satisfaction or settlement of, any proceeding,  claim or action,  and it is ever
determined  that  any  of  the  Indemnification   Exclusions  apply,  then  such
Indemnified  Party  shall  immediately  reimburse  SIGA for all  such  expenses,
together with interest thereon at prevailing rates.

      13.  Certain  Conditions.  The  rights of Cooper  and  Schein  under  this
Agreement,  including,  without limitation, (i) the release of Cooper and Schein
by Drapkin  contained in Section 10 hereof,  (ii) SIGA's  obligation  to pay the
fees for counsel to Cooper and Schein  contained in Section 9 hereof,  (iii) the
adjustments to certain options held by Cooper and Schein,  pursuant to Section 8
hereof,  (iv) the right of Cooper  and  Schein to  Transfer  certain  securities
during the Lock-Up  Period,  as  provided in  Subsection  6(a)  hereof,  and (v)
Drapkin's,  Cerrone's,  Constance's and Rose's respective  obligations regarding
restrictions on Transfer of certain  securities  during the Lock-Up  Period,  as
provided in Subsection 6(b), are all subject to the following conditions:

            (a)   Drapkin and his designees shall be elected to the Board;

            (b) Cooper, Schein and each Resigning Director shall resign from the
Board and from any and all offices held by such Resigning Director with SIGA, in
each case, at no cost to SIGA except to the extent expressly provided herein;
and

            (c) Any consulting agreements or other arrangements between SIGA and
any entity controlled by Cooper or Schein, including, without limitation, Prism
Ventures LLC, that Drapkin requests to be terminated shall be terminated at no
cost to SIGA.

      14.  Securityholdings  of Drapkin,  Cerrone,  Constance and Rose.  Each of
Drapkin, Cerrone, Constance nor Rose represents and warrants that, except as set
forth on Schedule  14, such Party does not  beneficially  own any Common  Stock,
Convertibles  or other  securities of SIGA,  excluding any such  securities with
respect to which such Party may be deemed  the  beneficial  owner  solely as the
holder of a proxy with respect thereto.

      15. Schedule 14f-1.  Cooper,  Schein and SIGA shall cause a Schedule 14f-1
Information Statement regarding the transactions contemplated by this Agreement,
in form and substance  reasonably  satisfactory to Drapkin, to be filed with the
Securities and Exchange

                                       8



Commission and transmitted to the stockholders of SIGA at least 10 days prior to
the Effective Date.

      16. Successors and Assigns. All authority herein conferred or agreed to be
conferred  shall  survive the death or  incapacity  of any Party  hereto and any
obligations   of  any  Party   shall  be  binding   upon  the  heirs,   personal
representatives, successors, and assigns of such Party.


                                       9



            If this reflects your understanding of the Agreement, please sign
below and return a copy of this letter to the undersigned.


                                    ---------------------------------
                                    Donald G. Drapkin

Accepted and Agreed to:


SIGA TECHNOLOGIES, INC.


By:  ______________________
    Name:
    Title:


- ----------------------
Gabriel M. Cerrone


- ----------------------
Thomas E. Constance


- ----------------------
Eric A. Rose, M.D.


- ----------------------
Judson A. Cooper


- ----------------------
Joshua D. Schein, Ph.D.


                                       10



                                                                       EXHIBIT A

                                     FORM OF
                                 MUTUAL RELEASE

      THIS MUTUAL RELEASE (this "Mutual Agreement"), made and entered into as of
this __ day of April, 2001, by and between SIGA Technologies, Inc., 420
Lexington Avenue, Suite 620, New York, New York 10170, and [Joshua Schein,
[INSERT ADDRESS]] [Judson Cooper, [INSERT ADDRESS]] {Jeffrey Rubin {INSERT
ADDRESS}}{Eric I. Richman {INSERT ADDRESS}} {Thomas N. Lanier {INSERT ADDRESS}}.
As used throughout this Agreement: "Company" refers to SIGA Technologies, Inc.,
together with its their past and present parents, subsidiaries, and affiliates,
and each of their respective past and present officers, directors, agents,
employees, successors and assigns, in both their individual and corporate
capacities; and "Executive" refers to [Joshua Schein] [Judson Cooper] {Jeffrey
Rubin} {Eric I. Richman} {Thomas N. Lanier}, his heirs, executors,
administrators, agents, successors, assigns and dependents.

      WHEREAS, Executive is serving [as the [Chief Executive Officer]
[Chairman and Executive Vice President] of SIGA Technologies, Inc.] {[[and]
as a member of the Board of Directors of SIGA Technologies, Inc.]}; and

      WHEREAS, by mutual agreement between Executive and the Company, Executive
has agreed to resign as an employee, officer and director of the Company
effective as of the date hereof; and

      WHEREAS, SIGA Technologies, Inc., [Executive,] [{the other(s) of Cooper
and/or Schein}] Gabriel M. Cerrone, Thomas E. Constance, Donald G. Drapkin
and Eric A. Rose, M.D. have entered into a letter agreement of dated as of
March 30, 2001 (the "Restructuring Agreement") that contemplates the
execution and delivery of this Agreement.

      NOW, THEREFORE, for and in consideration of the mutual promises, covenants
and obligations contained herein, the parties hereto agree as follows:

      Section 1    Release of Claims by Executive.

                  (a) Except as necessary to enforce the terms of this Mutual
Release, [the Separation Agreement dated as of March 30, 2001 among the parties
hereto (the "Separation Agreement"), and the Restructuring Agreement,] and in
exchange for and in consideration of the promises, covenants and agreements set
forth herein [and therein], Executive hereby releases the Company to the maximum
extent permitted by law from any and all manner of claims, demands, causes of
action, obligations, damages, or liabilities whatsoever of every kind and
nature, at law or in equity, known or unknown, and whether or not discoverable,
which Executive has or may have for any period prior to and including the date
of his execution of this Mutual Release, including, but not limited to, any
claim of defamation, wrongful discharge, breach of contract, claims for unpaid
wages, claims arising under or related to [the Employment Agreement (as defined
in the Separation Agreement)] {such Executive's service ("Board Service") as a
member of the Board of Directors of the Company} and claims of discrimination
under the Age Discrimination in

                                       11



Employment  Act of 1967 and all other  federal,  state and local  laws,  and any
claim for attorneys' fees or costs.

                  (b) Executive represents that he does not have any claim,
action or proceeding pending against the Company or which arises out of his
[employment by the Company] {Board Service}. Executive represents and warrants
that he has not assigned or subrogated any of his rights, claims and causes of
action, including any claims referenced in this Agreement, or authorized any
other person or entity to assert such claim or claims on his behalf, and he
agrees to indemnify and hold harmless the Company against any assignment of said
rights, claims and/or causes of action.

                  (c) Executive represents and warrants that[, other than (i)
the Employment Agreement, as modified by the Separation Agreement, and (ii) as
provided for under the Restructuring Agreement,] Executive is not party to any
agreement or arrangement respecting employment by the Company.

      Section 2 Release of Claims by the Company. Except as necessary to enforce
the terms of this Mutual Release, [the Separation Agreement and the
Restructuring Agreement,] and in exchange for and in consideration of the
promises, covenants and agreements set forth herein [and therein], the Company
hereby releases Executive to the maximum extent permitted by law from any and
all manner of claims, demands, causes of action, obligations, damages, or
liabilities whatsoever of every kind and nature, at law or in equity, known or
unknown, and whether or not discoverable, arising out of Executive's [employment
by the Company] {Board Service} which the Company has or may have for any period
prior to and including the date of the execution of this Mutual Release;
provided, however, that the Company does not release herein any claims the
Company may now or in the future have against Executive for acts of intentional
misconduct committed by Executive during Executive's [employment with the
Company] {Board Service}.

      Section 3   Acknowledgements.

                  (a) Executive acknowledges that he has read and understands
the terms of this Mutual Release and has voluntarily agreed to these terms
without coercion or undue persuasion by the Company.

                  (b) Executive acknowledges that he has been advised to consult
with an attorney prior to executing this Mutual Release. Executive also
acknowledges that he has had an adequate opportunity to review this Mutual
Release before its execution.

                  (c) Executive acknowledges that he has been afforded an
opportunity to take at least twenty-one (21) days to consider this Mutual
Release and has been advised to consult with the attorneys of his choice prior
to executing this Mutual Release. Executive further acknowledges that he will
have a period of seven (7) calendar days following his execution of this Mutual
Release in which to revoke his consent, and that such revocation will be
effective only if received in writing by Kramer Levin Naftalis & Frankel LLP,
919 Third Avenue, New York, New York, 10022, Attention: David M. Zlotchew, Esq.,
on or before the expiration of this seven (7) day period. This Mutual Release
will not become effective or enforceable until the revocation period has
expired.

                                       12



                  IN WITNESS WHEREOF, the parties hereto have executed this
Mutual Release as of the date first written above.


                                       SIGA TECHNOLOGIES, INC.


                                       By:
                                          ------------------------------------




                                       _______________________________________
                                       [Joshua Schein]
                                       [Judson Cooper]
                                       {Jeffrey Rubin}
                                       {Eric I. Richman}
                                       {Thomas N. Lanier}


                                       13




                                                                       EXHIBIT B
                                     FORM OF
                                IRREVOCABLE PROXY

            The undersigned ("Stockholder"), being the holder of _____ shares of
common stock, $.0001 par value per share, of SIGA Technologies, Inc., a Delaware
corporation (the "Company") (together with any shares of capital stock of the
Company which the undersigned may acquire subsequent to the date hereof, the
"Shares"), does hereby irrevocably constitute and appoint Donald G. Drapkin
("Proxyholder") Stockholder's true and lawful attorney, agent and proxy, to vote
and otherwise act, or give written consent in lieu thereof, any or all of the
Shares on Stockholder's behalf and in Stockholder's name, place and stead, as
Stockholder's proxy and representative, and otherwise to exercise all voting
rights and to enter into agreements, on Stockholder's behalf, with respect to
the Shares in the same manner and to the same extent as if Proxyholder were the
sole and absolute owner thereof in Proxyholder's own right; and full power and
authority are hereby conferred upon Proxyholder to do all such things within the
power of a shareholder as may be incident to the foregoing, including without
limitation to attend meetings of the shareholders of the Company or any
continuations or adjournments thereof on Stockholder's behalf, with full power
of substitution and revocation and with all the powers Stockholder would possess
if personally present thereat, or to consent in writing on Stockholder's behalf
to any action of the shareholders of the Company.

            Any proxy or proxies heretofore given by the undersigned to any
person or persons with respect to the foregoing matters are hereby revoked. This
Irrevocable Proxy shall be effective from the date hereof until April 16, 2003
(the "Term"), except as expressly provided below.

            THIS IRREVOCABLE PROXY SHALL BE DEEMED COUPLED WITH AN INTEREST AND
IS IRREVOCABLE, AND STOCKHOLDER RETAINS NO RIGHT TO CANCEL, RESCIND, QUALIFY OR
MODIFY THIS PROXY IN ANY RESPECT DURING THE TERM.

            This proxy shall remain in full force and effect and be binding upon
any donee, transferee or assignee of Stockholder, except to the extent that
Stockholder's entire interest in any Shares are transferred in accordance with
the terms of the letter agreement dated as of March 30, 2001 among Proxyholder,
the Company, Stockholder, Gabriel M. Cerrone, Thomas E. Constance, Eric A. Rose,
M.D. and [the other of Cooper or Schein].

Dated as of April 16, 2001

                                    -----------------------------
                                    [Stockholder's name]


                                       14




                                                                       Exhibit J

                                LOCK-UP AGREEMENT

            This LOCK-UP AGREEMENT (this "Agreement") is entered into as of
January __, 2001, by and between Donald G. Drapkin ("Drapkin") and Vincent
Fischetti ("Fischetti").

            WHEREAS, Drapkin and Fischetti desire to enter into the "lock-up"
arrangements contained in this Agreement relating to securities of Siga
Technologies, Inc., a Delaware corporation, ("SIGA").

            NOW, THEREFORE, in consideration of the premises and the obligations
herein contained and for other consideration, the receipt and sufficiency of
which is hereby acknowledged, the parties hereto, intending to be legally bound,
agree as follows:

            1. Without the prior written consent of Drapkin, Fischetti shall
not, and shall cause his respective relatives and affiliates to not, directly or
indirectly, offer, sell, pledge, hypothecate, contract to sell, grant any option
to purchase, short or otherwise dispose (or announce any offer, sale, contract
of sale or other disposition) of (collectively, "Transfer") any shares, or any
interest in any shares, of common stock, par value $.0001 per share ("Common
Stock") or other shares of capital stock of SIGA or any Convertibles (as defined
below) during the period commencing on the date of this Agreement and ending on
July 31, 2003 (the "Lock-Up Period").

            2. Notwithstanding anything to the contrary in Paragraph 1, if
Drapkin Transfers any Common Stock or Convertibles during the Lock-Up Period,
Fischetti shall not be prohibited from Transferring the same proportion of
Fischetti's Common Stock or Convertibles, as the case may be, as Drapkin
Transfers; provided, that Fischetti so Transfers in the same manner as Drapkin.

            3. In addition, the Parties shall, (i) with respect to any shares of
Common Stock for which Fischetti is the record holder, cause the transfer agent
for SIGA to note stop transfer instructions with respect to such shares of
Common Stock on the transfer books of SIGA and, (ii) with respect to any shares
of Common Stock for which Fischetti is the "beneficial owner" (within the
meaning of Rule 13d-3 promulgated under the Securities Exchange Act of 1934, as
amended) but not the record holder, cause the record holder of such shares of
Common Stock to cause the transfer agent for SIGA to note stop transfer
instructions with respect to such shares of Common Stock on the transfer books
of SIGA.

            4. During the Lock-Up Period, Fischetti shall be the holder of
record of every share of Common Stock that may be deemed beneficially owned by
him.

            5. The provisions of this Agreement may be waived or modified by a
writing signed by Drapkin; provided, however, that no modification of this
Agreement may place further restrictions on Fischetti's ability to Transfer
securities of SIGA without Fischetti's written consent thereto.




            IN WITNESS WHEREOF, the parties hereto have duly executed this
Agreement as of the date first above written.



                                    /s/ Vincent Fischetti
                                    ------------------------------------
                                    Vincent Fischetti



Accepted and Agreed to:


_______________________
Donald G. Drapkin