As filed with the Securities and Exchange Commission on May 10, 2000
                                                          Registration No. 333-
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    FORM S-3
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                           ---------------------------
                            SIGA Technologies, Inc.
            (Exact Name of Registrant as Specified in Its Charter)
                           ---------------------------
                 Delaware                      13-3864870
      (State or Other Jurisdiction of       (I.R.S. Employer
      Incorporation or Organization)       Identification No.)
                              420 Lexington Avenue
                                    Suite 620
                            New York, New York 10170
                                 (212) 672-9100
         (Address,  including zip code,  and telephone  number,  including  area
             code, of Registrant's principal executive office)
                           ----------------------------
                             Joshua D. Schein, Ph.D.
                             Chief Executive Officer
                             SIGA Technologies, Inc.
                              420 Lexington Avenue
                                    Suite 620
                            New York, New York 10170
                           (Name and Address of Agent
                                  For Service)
                                 (212) 672-9100

         (Telephone Number, Including Area Code, of Agent For Service)
                                   Copies to:
                            Lawrence B. Fisher, Esq.
                       Orrick, Herrington & Sutcliffe LLP
                                666 Fifth Avenue
                            New York, New York 10103
                  (212) 506-5000 (Phone) (212) 506-5151 (Fax)

   Approximate date of commencement of proposed sale to the public: From time to
time as determined by the Selling Stockholders.

   If the only  securities  being  registered  on this  Form are  being  offered
pursuant to dividend or interest  reinvestment plans, please check the following
box. [__]

   If any of the securities  being registered on this Form are to be offered on
a delayed or continuous  basis  pursuant to Rule 415 under the  Securities  Act
of 1933,  other than  securities  offered only in  connection  with dividend or
interest reinvestment plans, check the following box.  [X]

   If this  Form is filed to  register  additional  securities  for an  offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list  the  Securities  Act  registration  statement  number  of the  earlier
effective registration statement for the same offering. [__]

   If this Form is a  post-effective  amendment  filed  pursuant  to Rule 462(c)
under the  Securities  Act,  check the following box and list the Securities Act
registration  statement number of the earlier effective  registration  statement
for the same offering. [__]

   If delivery of the  prospectus  is expected to be made  pursuant to Rule 434,
please check the following box. [__]
                         CALCULATION OF REGISTRATION FEE
===============================================================================
                                         Proposed    Proposed
                            Amount       Maximum      Maximum     Amount of
 Title of Securities To      To Be       Offering    Aggregate   Registration
     Be Registered       Registered(1)  Price Per    Offering        Fee
                                        Share (2)    Price (2)
- -------------------------------------------------------------------------------
Common Stock, $0.0001      2,833,391      $4.16     $11,786,907     $3,112
par value                   shares
- -------------------------------------------------------------------------------
(1)   Pursuant to Rule 416 under the  Securities  Act of 1933, as amended,  this
      registration  statement also covers such indeterminate number of shares of
      common stock as may be required to prevent  dilution  resulting from stock
      splits, stock dividends or similar events.

(2)   Estimated   solely  for  the  purpose  of  computing  the  amount  of  the
      registration  fee,  based on the  average of the high and low  prices for
      SIGA Technologies,  Inc.'s common stock as reported on the Nasdaq SmallCap
      Market on May 8, 2000 in accordance  with Rule 457(c) under the Securities
      Act of 1933, as amended.

   The  Registrant  hereby  amends this  registration  statement on such date or
dates as may be necessary to delay its effective date until the Registrant shall
file a further  amendment  which  specifically  states  that  this  registration
statement shall  thereafter  become effective in accordance with Section 8(a) of
the Securities  Act of 1933 or until this  registration  statement  shall become
effective on such date as the  Commission,  acting pursuant to Section 8(a), may
determine.


THE  INFORMATION  IN THIS  PRELIMINARY  PROSPECTUS  IS NOT  COMPLETE  AND MAY BE
CHANGED. THESE SECURITIES MAY NOT BE SOLD UNTIL THE REGISTRATION STATEMENT FILED
WITH THE  SECURITIES  AND EXCHANGE  COMMISSION  IS EFFECTIVE.  THIS  PRELIMINARY
PROSPECTUS  IS NOT AN OFFER  TO SELL  NOR  DOES IT SEEK AN  OFFER  TO BUY  THESE
SECURITIES IN ANY JURISDICTION WHERE THE OFFER OR SALE IS NOT PERMITTED.

                   Subject to completion, dated May 10, 2000




                                2,833,391 Shares

                             SIGA Technologies, Inc.

                                  Common Stock

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

      Shares of common stock of SIGA  Technologies,  Inc.  are being  offered by
this  prospectus.  The  shares  will  sold  from  time to  time  by the  selling
stockholders  named  in this  prospectus.  The  prices  at  which  such  selling
stockholders  may sell the shares will be  determined by the  prevailing  market
price for the shares or in  negotiated  transactions.  We will not  receive  any
proceeds from the sale of shares of common stock by the selling stockholders but
we will receive  proceeds  from the exercise of warrants  held by certain of the
selling stockholders.  Our shares are traded on the Nasdaq SmallCap Market under
the symbol  "SIGA."  The last  reported  sale price for the shares on the Nasdaq
SmallCap Market on May 8, 2000 was $4.06 per share.

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

      Investing in the shares involves a high degree of risk.  For more
information, please see "Risk Factors" beginning on page 7.

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

      Neither the  Securities and Exchange  Commission nor any state  securities
commission has approved or disapproved of these securities or determined whether
this prospectus is truthful or complete. Any representation to the contrary is a
criminal offense.

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


                  The date of this prospectus is May 10, 2000








                                TABLE OF CONTENTS

                                                                Page

About this Prospectus..........................................   3
Where You Can Find More Information............................   3
Forward-Looking Statements.....................................   4
About SIGA Technologies, Inc...................................   5
Recent Developments............................................   6
Risk Factors...................................................   7
Use of Proceeds................................................  10
Selling Stockholders...........................................  11
Plan of Distribution...........................................  14
Legal Matters..................................................  17
Experts........................................................  17


                                       2

                              ABOUT THIS PROSPECTUS

      This prospectus is part of a registration statement that we filed with the
Securities  and Exchange  Commission  (the  "SEC").  The  prospectus  relates to
2,833,391  shares of our common  stock which the selling  stockholders  named in
this  prospectus  may sell from  time to time.  We will not  receive  any of the
proceeds  from these sales but we will  receive  proceeds  from the  exercise of
warrants  held  by  certain  selling  stockholders.  We have  agreed  to pay the
expenses  incurred in  registering  the shares,  including  legal and accounting
fees.

      The shares have not been registered under the securities laws of any state
or other  jurisdiction  as of the date of this  prospectus.  Brokers  or dealers
should  confirm the existence of an exemption  from  registration  or effectuate
such registration in connection with any offer and sale of the shares.

      This  prospectus  describes  certain risk factors that you should consider
before purchasing the shares. See "Risk Factors" beginning on page 7. You should
read this prospectus  together with the additional  information  described under
the heading "Where You Can Find More Information."

                       WHERE YOU CAN FIND MORE INFORMATION

      Federal  securities  law  requires  us to file  information  with  the SEC
concerning our business and  operations.  We file annual,  quarterly and special
reports,  proxy statements and other  information with the SEC. You can read and
copy these documents at the public reference  facility  maintained by the SEC at
Judiciary Plaza, 450 Fifth Street, NW, Room 1024, Washington,  DC 20549. You can
also copy and inspect such reports,  proxy  statements and other  information at
the regional offices of the SEC located at Seven World Trade Center, 13th Floor,
New York,  New York 10048 and 500 West  Madison  Street,  Suite  1400,  Chicago,
Illinois 60661.

      Please  call the SEC at  1-800-SEC-0330  for  further  information  on the
public  reference rooms. Our SEC filings are also available to the public on the
SEC's web site at  http://www.sec.gov.  You can also inspect our reports,  proxy
statements and other information at the offices of the Nasdaq Stock Market.

      The SEC allows us to  "incorporate  by reference" the  information we file
with it,  which  means  that we can  disclose  important  information  to you by
referring  you to  those  documents.  The  information  that we  incorporate  by
reference is considered  to be part of this  prospectus,  and later  information
that  we  file  with  the SEC  will  automatically  update  and  supersede  this
information.  We  incorporate  by reference the  documents  listed below and any
future filings made with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"):

     1. Our Annual Report on Form 10-KSB/A for the year ended December 31, 1999.

     2.  The  Definitive  Proxy  Statement  for the  Annual  Meeting  of SIGA on
Schedule 14A, dated January 14, 2000.

                                       3


      3. The  description  of our common  stock  contained  in our  registration
statement on Form 8-A under Section 12 of the Exchange Act,  dated  September 5,
1997,  including any amendment or reports filed for the purpose of updating such
description.

      This prospectus is part of a registration  statement we filed with the SEC
(Registration No.  333-______).  You may request a free copy of any of the above
filings by writing or calling Thomas  Konatich,  Chief Financial  Officer,  SIGA
Technologies,  Inc., 420 Lexington Avenue,  Suite 620, New York, New York 10170,
(212) 672-9100.

      You should  rely only on the  information  incorporated  by  reference  or
provided in this  prospectus or any supplement to this  prospectus.  We have not
authorized  anyone else to provide you with different  information.  The selling
stockholders  should  not make an offer of these  shares in any state  where the
offer is not  permitted.  You  should not assume  that the  information  in this
prospectus or any supplement to this prospectus is accurate as of any date other
than the date on the cover page of this prospectus or any supplement.

                           FORWARD-LOOKING STATEMENTS

      This prospectus and the other reports we have filed with the SEC,  contain
"forward-looking statements" within the meaning of Section 27A of the Securities
Act of 1933, as amended (the "Securities  Act"), and Section 21E of the Exchange
Act. The words or phrases  "can be",  "expects",  "may  affect",  "may  depend",
"believes", "estimate", "project", and similar words and phrases are intended to
identify such forward-looking  statements.  Such forward-looking  statements are
subject to various known and unknown risks and  uncertainties and we caution you
that any forward-looking  information  provided by or on behalf of Siga is not a
guarantee of future performance. Our actual results could differ materially from
those anticipated by such forward-looking statements due to a number of factors,
some of which are beyond our  control,  in addition to those risks  discussed in
"Risk  Factors"  in this  prospectus  and in our  other  public  filings,  press
releases  and  statements  by our  management,  including  (i) the  volatile and
competitive nature of the biotechnology and Internet industries, (ii) changes in
domestic  and foreign  economic and market  conditions,  and (iii) the effect of
federal,  state and foreign  regulation on our businesses.  All  forward-looking
statements are current only as of the date on which such  statements  were made.
We do not  undertake  any  obligation  to  publicly  update any  forward-looking
statement to reflect  events or  circumstances  after the date on which any such
statement is made or to reflect the occurrence of unanticipated events.

                                       4


                          ABOUT SIGA TECHNOLOGIES, INC.

      SIGA  Technologies,  Inc. is a development stage company with interests in
biotechnology  and the Internet.  Siga Research Labs,  (SRL), our  biotechnology
division,  is focused on the discovery,  development  and  commercialization  of
vaccines, antibiotics and novel anti-infectives for serious infectious diseases.
SRL's lead vaccine  candidate  is for the  prevention  of group A  streptococcal
pharyngitis  or "strep  throat." SRL is developing a technology  for the mucosal
delivery of its vaccines  which may allow those  vaccines to activate the immune
system at the mucus lined surfaces of the body -- the mouth, the nose, the lungs
and the  gastrointestinal  and urogenital  tracts -- the sites of entry for most
infectious agents.  SRL's  anti-infectives  programs,  aimed at the increasingly
serious  problem  of drug  resistance,  are  designed  to block the  ability  of
bacteria to attach to human tissue, the first step in the infection process.

      We are currently  developing,  PeerFinder(TM),  a third generation instant
messenger,  which we believe will make the Internet more interactive by enabling
meaningful  conversation within peer groups or between like-minded  individuals.
As a complement to users' normal  surfing  habits,  PeerFinder(TM)  will provide
instant messaging  technology for peer-to-peer  communication  across Web sites,
servicing the Internet's  rapidly growing collection of online  communities.  By
combining the search for content with real-time conversation, users will be able
to easily locate  information,  transact  business,  solicit  product reviews or
simply converse with like-minded individuals on the topics of their interest.

Our Technologies

      Vaccine Technologies:  Mucosal Immunity and Vaccine Delivery

      Using  proprietary  technology  licensed from The  Rockefeller  University
("Rockefeller"), Siga is developing certain commensal bacteria ("commensals") as
a means to deliver  mucosal  vaccines.  Commensals  are harmless  bacteria  that
naturally  inhabit the body's  surfaces  with  different  commensals  inhabiting
different  surfaces,  particularly the mucosal surfaces.  Our vaccine candidates
utilize genetically  engineered commensals to deliver antigens from a variety of
pathogens to the mucosal immune system.

PeerFinder(TM)

      PeerFinder(TM) is an Internet-based application that is being developed to
allow registered  users viewing any given Web site to see and communicate  with:
(i) all other members of the same peer group  wherever they are on the Web, (ii)
all other registered users simultaneously viewing the same site and (iii) all of
the people in the  registered  users  buddy list.  The product  will enable both
group and private  communication in a small discussion box that overlays the Web
site being  viewed.  The product is being  designed to facilitate a more natural
form of  conversation  that is both content driven and  spontaneous.  We believe
PeerFinder(TM)  will make the Internet  more  interactive  by enabling  group or
private  communication that is not restricted to any particular Web site or chat
room, but will complement the users' normal Web browsing habits.  PeerFinder(TM)
is expected to have the following features:

      Peer groups - Users will sign up with a particular  peer or interest group
when they  register.  Users will be  notified  when other  members of their peer
groups are online and can


                                       5


communicate  with them even if they are at a different  Web site.  Users will be
able to converse with their peers simultaneously or in one-on-one environments.

      Siteseers - Users will be notified of other  PeerFinder(TM)  users who are
on the same Web site they are on and will be able to communicate with each other
in either group or one-to-one discussion.

      Buddy list - Users will be notified when their self selected "buddies" are
online and will be able to communicate with them no matter where they are on the
Web.

      Video, Audio, and Multimedia  Streaming - Users will be able to select one
of several video,  audio or multimedia  feeds within the  PeerFinder(TM)  box to
watch and/or listen to.

      Our principal executive offices are located at 420 Lexington Avenue, Suite
620, New York,  New York 10170.  Our  telephone  number is (212)  672-9100.  The
information  included  on our  web  site  is not  intended  to be  part  of this
prospectus.

                               RECENT DEVELOPMENTS

     In January, 2000 we completed a private placement of an aggregate principal
amount of $1,500,000  6%  convertible  debentures  and  1,043,478  warrants.  We
received net proceeds of $1,499,674  from the total  $1,552,174  gross proceeds.
The debentures are convertible into common stock at $1.4375 per share.  Interest
at the rate of 6% per annum is  payable  on the  principal  of each  convertible
debenture on conversion or at maturity.  At our option,  interest may be paid in
cash or common stock at the conversion price then in effect. The warrants have a
term of five years and are  exercisable at $3.4059 per share. We can require the
holder  to  exercise  the  warrants   within  five  days  under  the   following
circumstances:  (i) a registration statement is effective;  and (ii) the closing
bid price for our common stock for each of any 15 consecutive trading days is at
least  200% of the  exercise  price of such  warrants.  If the  holder  does not
exercise  the warrants  after notice is given,  the  unexercised  warrants  will
expire.  In connection  with the placement of the  debentures  and warrants,  we
recorded debt discount of approximately $1.0 million. This amount represents the
value of the warrants  calculated using the  Black-Scholes  valuation model. The
discount will be amortized over the term of debentures.

      In  connection  with this  transaction,  we issued  warrants to purchase a
total of  275,000  shares of our  common  stock to the  placement  agent and the
investors' counsel (or their respective  designees).  These warrants have a term
of five years and are exercisable at $1.45 per share.

      The  terms  of the  convertible  debentures  and the  warrants  issued  in
connection  with  the  January  2000  transaction  specify  that,  with  limited
exceptions, a holder cannot convert its debenture or exercise its warrant to the
extent  that such  conversion  or  exercise  would  result in the holder and its
affiliates then owning more than 9.99% of the then outstanding common stock. The
limited exceptions include the existence of a tender offer for our common stock.

      On March 28, 2000 we  completed a private  placement  of an  aggregate  of
600,000 shares of common stock and 450,000 warrants. We received net proceeds of
$2,883,000 from the total gross proceeds of $3,000,000. The warrants have a term
of three years; 210,000 warrants are exercisable at $5.00 per share, 120,000 are
exercisable at $6.375 per share and 120,000 are  exercisable at $6.90 per share.
Under certain circumstances, we can redeem the warrants.


                                       6

                                  RISK FACTORS

      In this section,  we highlight the significant  risks  associated with our
business and operations. Investing in our common stock involves a high degree of
risk.  You  should  be able  to bear a  complete  loss  of your  investment.  To
understand the level of risk, you should  carefully  consider the following risk
factors,  as well as the  other  information  found  in  this  prospectus,  when
evaluating an investment in the shares.

    WE HAVE INCURRED  OPERATING LOSSES SINCE OUR INCEPTION AND EXPECT TO INCUR
NET LOSSES AND NEGATIVE CASH FLOW FOR THE  FORESEEABLE  FUTURE.  We incurred net
losses of $2.2 million for the year ended  December  31, 1997,  $6.6 million for
the year ended  December 31, 1998 and $3.6  million for the year ended  December
31, 1999. As of December 31, 1999 and December 31, 1998, our accumulated deficit
was $14.7  million  and $11.0  million,  respectively.  We expect to continue to
incur significant  operating and capital  expenditures and, as a result, we will
need to generate significant revenues to achieve and maintain profitability.  We
cannot  guarantee that we will achieve  sufficient  revenues for  profitability.
Even if we do achieve profitability,  we cannot guarantee that we can sustain or
increase profitability on a quarterly or annual basis in the future. If revenues
grow slower than we anticipate, or if operating expenses exceed our expectations
or cannot be adjusted  accordingly,  our  business,  results of  operations  and
financial  condition  will be  materially  and adversely  affected.  Because our
strategy includes acquisitions of other businesses, acquisition expenses and any
cash used to make these acquisitions will reduce our available cash.

     UNCERTAINTY  OF  AVAILABILITY  OF  ADDITIONAL   FUNDING.  We  will  require
substantial  additional  funds to conduct and sponsor  research and  development
activities related to our biopharmaceutical and Internet businesses,  to conduct
pre-clinical and clinical testing, and to market our products. We intend to seek
such additional funding through collaborative arrangements and through public or
private financings.  There can be no asurance that additional  financing will be
available,  or, if available,  that such additional financing will be available,
or, if  available  that such  additional  financing  will be  available on terms
acceptable to us.

      WE ARE IN  VARIOUS  STAGES  OF  PRODUCT  DEVELOPMENT  AND  THERE CAN BE NO
ASSURANCE OF SUCCESSFUL COMMERCIALIZATION. Our research and development programs
are  at an  early  stage  of  development.  The  United  States  Food  and  Drug
Administration has not approved any of our biopharmaceutical product candidates.
Any drug candidates developed by us will require significant additional research
and development efforts,  including extensive  pre-clinical and clinical testing
and  regulatory  approval,  prior to  commercial  sale.  We  cannot  be sure our
approach to drug discovery  will be effective or will result in the  development
of any drug.  We cannot  expect that any drugs that do result from our  research
and development efforts will be commercially available for many years.

      WE HAVE LIMITED EXPERIENCE IN CONDUCTING PRE-CLINICAL TESTING AND CLINICAL
TRIALS. Even if we receive initially positive pre-clinical results, such results
do not mean that  similar  results  will be obtained in the later stages of drug
development,  such as additional  pre-clinical testing or human clinical trials.
All of our potential drug candidates are prone to the risks of failure  inherent
in pharmaceutical  product  development,  including the possibility that none of
our drug candidates will or can

o     be safe, non-toxic and effective;
o     otherwise meet applicable regulatory standards;
o     receive the necessary regulatory approvals;
o     develop into commercially viable drugs;

                                       7

o     be manufactured or produced economically and on a large scale;
o     be successfully marketed;
o     be reimbursed by government or private consumers; and
o     achieve customer acceptance.

      In  addition,  third  parties  may  preclude us from  marketing  our drugs
through  enforcement of their proprietary  rights. Or, third parties may succeed
in marketing equivalent or superior drug products.  Our failure to develop safe,
commercially  viable drugs would have a material adverse effect on our business,
financial condition and results of operations.

      WE FACE DIFFICULTIES  TYPICALLY ENCOUNTERED BY DEVELOPMENT STAGE COMPANIES
IN NEW AND RAPIDLY EVOLVING MARKETS BECAUSE OF OUR NEW INTERNET  INITIATIVE.  We
have  recently  begun  developing  PeerFinder(TM),  a third  generation  instant
messenger.  An investor  purchasing our common stock must therefore consider the
risks and  difficulties  frequently  encountered by early stage companies in new
and rapidly evolving markets,  such as online commerce.  These risks include our
ability to:

      o    develop our web site;
      o    acquire rights to content for our web site;
      o    create a customer base;
      o    respond to changes in a rapidly evolving and unpredictable business
           environment;
      o    maintain current and develop new strategic relationships;
      o    manage growth;
      o    continue to develop and upgrade our technology; and
      o    attract, retain and motivate qualified personnel.

We  cannot   assure  you  that  any  services  or  products   developed  by  us,
independently or with collaborative partners, will achieve market acceptance.

     THE  BIOPHARMACEUTICAL  AND INTERNET MESSENGING MARKETS IN WHICH WE COMPETE
AND WILL  COMPETE  ARE HIGHLY  COMPETITIVE.  The  biopharmaceutical  industry is
characterized by rapid and significant  technological  change.  Our success will
depend on our  ability to develop and apply our  technologies  in the design and
development of our product candidates and to establish and maintain a market for
our product candidates.  There also are many companies, both public and private,
including major pharmaceutical and chemical companies, specialized biotechnology
firms,  universities  and other  research  institutions  engaged  in  developing
pharmaceutical  and  biotechnology   products.  Many  of  these  companies  have
substantially greater financial,  technical, research and development, and human
resources than us.  Competitors may develop products or other  technologies that
are more  effective  than any that are being  developed  by us or may obtain FDA
approval for products more rapidly than us. If we commence  commercial  sales of
products,  we still must  compete in the  manufacturing  and  marketing  of such
products,  areas in which we have no  experience.  Many of these  companies also
have manufacturing  facilities and established marketing capabilities that would
enable such companies to market competing  products through existing channels of
distribution.  The Internet messenging market is highly competitive. This market
may experience pricing and margin pressure,  which as a result,  could adversely
affect our operating results and financial position. A number of companies offer
products and services  that target the same market that we target.  The Internet
market is characterized by an increasing  number of entrants due to low start-up
costs.  Some of our competitors and potential  competitors have larger technical
staffs,  more  established  and larger  marketing  and sales  organizations  and
significantly  greater financial  resources than us. Our competitors may develop
products that are superior to ours or that achieve  greater  market  acceptance.
Our future  success will depend  significantly  upon our ability to increase our
share of our target market and to sell additional products, product enhancements
and services to our customers.  We may not be able to compete successfully,  and
competition may result in decreases in:

        o the prices we receive for our products and services;
        o our revenues;
        o our profit margins; or
        o our market share.

                                       8


     Any of these decreases  could adversely  affect our business and results of
operations.

     IN ORDER TO COMPETE SUCCESSFULLY,  WE MUST KEEP PACE WITH THE RAPID CHANGES
INVOLVING  TECHNOLOGY AND THE INTERNET.  The Internet and technology industry is
characterized by rapid technological advances,  changes in customer requirements
and frequent new product and services introductions and enhancements. Our future
success  will  depend  upon our ability to enhance  our  proposed  products  and
services and to develop and  introduce  new products and services that keep pace
with  technological  developments,  respond  to  the  growth  in  the  Internet,
encompass  evolving  customer  requirements and achieve market  acceptance.  Any
failure  on our  part to  anticipate  or  respond  adequately  to  technological
developments  and customer  requirements,  or any significant  delays in product
development  or  introduction,  could  result  in  a  loss  of  competitiveness,
revenues,  profit  margins  or  market  share.  There is no  assurance  that new
products  or  product   enhancements   which  we  develop  will  achieve  market
acceptance.

     WE MAY BE SUBJECT TO LITIGATION  AND  INFRINGEMENT  CLAIMS.  The technology
that we use to  develop  our  products,  and those  that we  incorporate  in our
products, may be subject to claims that they infringe the patents or proprietary
rights  of  others.  The risk of this  occurring  will tend to  increase  as the
biotechnology and software  industries expand, more patents are issued and other
companies attempt to develop mucosal vaccines and anti-infectives programs.

                                        9


      As is  typical  in the  biotechnology  and  software  industries,  we have
received, and we will probably receive in the future, notices from third parties
alleging patent  infringement.  We believe that we are not infringing the patent
rights of any such third party.

      We  may,   however,   be  involved  in  future  lawsuits  alleging  patent
infringement  or other  intellectual  property rights  violations.  In addition,
litigation may be necessary to:

      o    assert claims of infringement;

      o    enforce our patents;

      o    protect our trade secrets or know-how; or

      o    determine the enforceability, scope and validity of the proprietary
           rights of others.

      We may be unsuccessful in defending or pursuing these lawsuits. Regardless
of the  outcome,  litigation  can be very  costly  and can  divert  management's
efforts. An adverse  determination may subject us to significant  liabilities or
require us to seek licenses to other parties' patents or proprietary  rights. We
may also be restricted or prevented from  manufacturing or selling our products.
Further,  we may not be able to obtain  the  necessary  licenses  on  acceptable
terms, if at all.

      WE MAY HAVE  DIFFICULTY  MANAGING  OUR  GROWTH.  We expect to  continue to
experience  significant  growth in the number of our  employees and the scope of
our operations. This growth has placed, and may continue to place, a significant
strain on our management and operations.  Our ability to manage this growth will
depend  upon our  ability  to broaden  our  management  team and our  ability to
attract, hire and retain skilled employees.  Our success will also depend on the
ability of our officers and key  employees to continue to implement  and improve
our operational and other systems and to hire, train and manage our employees.

      WE DEPEND ON KEY EMPLOYEES IN A COMPETITIVE  MARKET FOR SKILLED PERSONNEL.
We are highly dependent on the principal  members of our management,  operations
and scientific staff,  including Joshua D. Schein,  our Chief Executive Officer.
The loss of any of these persons'  services would have a material adverse effect
on  our  business.  We  have  entered  into  employment  agreements  with  seven
individuals who we consider to be key employees. We do not maintain a key person
life insurance policy on the life of any employee.

      Our future  success also will depend in part on the  continued  service of
our key scientific,  software,  bioinformatics and management  personnel and our
ability to identify,  hire and retain additional  personnel,  including customer
service,  marketing  and sales staff.  We  experience  intense  competition  for
qualified  personnel.  We may not be able to  continue  to  attract  and  retain
personnel necessary for the development of our business.

      OUR  ACTIVITIES  INVOLVE  HAZARDOUS   MATERIALS  AND  MAY  SUBJECT  US  TO
ENVIRONMENTAL  REGULATORY  LIABILITIES.   Our  biopharmaceutical   research  and
development  involves the controlled use of hazardous and radioactive  materials
and  biological  waste.  We are  subject  to  federal,  state and local laws and
regulations  governing the use, manufacture,  storage,  handling and disposal of
these materials and certain waste products.  Although we believe that our safety
procedures  for

                                       10


handling  and  disposing  of these  materials  comply  with  legally  prescribed
standards,  the risk of accidental  contamination or injury from these materials
cannot be completely  eliminated.  In the event of an accident, we could be held
liable for damages, and this liability could exceed our resources.

      We  believe  that  we are in  compliance  in all  material  respects  with
applicable  environmental  laws and  regulations  and currently do not expect to
make  material  additional  capital   expenditures  for  environmental   control
facilities in the near term.  However, we may have to incur significant costs to
comply with current or future environmental laws and regulations.

      SALES OF SHARES  ELIGIBLE  FOR FUTURE SALE COULD  IMPAIR OUR STOCK  PRICE.
Sales of a substantial number of shares of common stock in the public market, or
the perception that sales could occur,  could adversely  affect the market price
for our common stock.  This  offering  will result in  additional  shares of our
common stock being available on the public market. These factors could also make
it more difficult to raise funds through future offerings of common stock.

                                 USE OF PROCEEDS

      The net proceeds from the sale of the  securities  will be received by the
selling  stockholders.  We will not receive any of the proceeds from the sale of
the securities by the selling  stockholders.  We will receive  proceeds from the
exercise of the warrants held by certain of the selling stockholders.


                                       11




                              SELLING STOCKHOLDERS

      The table below sets forth information  regarding  ownership of our common
stock by the  selling  stockholders  on March 20,  2000 and the shares of common
stock  to be  sold  by them  under  this  prospectus.  Beneficial  ownership  is
determined in accordance with SEC rules and includes voting or investment  power
with respect to the securities.  Except as indicated by footnote, and subject to
applicable  community  property  laws,  the persons named in the table have sole
voting and investment  power with respect to all shares of common stock shown as
beneficially  owned by them.  SEC  rules  require  that the  number of shares of
common stock  outstanding  used in  calculating  the  percentage for each listed
person includes the shares of common stock underlying convertible debentures and
warrants  held by such person that are  exercisable  within 60 days of March 20,
2000. In the case of selling  stockholders who own convertible  debentures,  the
number of shares owned prior to the offering includes the number of shares which
would be issued  upon  conversion  in payment of all  accrued  interest  through
maturity in January  2002.  Therefore,  the number of shares of common stock for
some listed persons may include  shares that are not subject to purchase  during
the 60 day period.  The number of shares  included in this table for some of the
selling  stockholders  may ultimately be more than the number of shares actually
held by such selling stockholders. The number of shares registered for resale by
each of Donald G. Drapkin,  Howard Gittis,  Lenore Katz, J. Jay Lobell, Frank J.
and Mary Ann Loccisano,  Alfons Melohn and Midnight Magic Investments under this
prospectus is equal to 110% of the amount  specified in the table below, to take
into  account  certain  possible  variations  in  the  conversion  rate  of  the
convertible debentures owned by each of such selling stockholders.

      We  have  filed  with  the  SEC,  under  the  Securities  Act of  1933,  a
registration  statement on Form S-3, of which this prospectus forms a part, with
respect to the resale of the securities from time to time on the Nasdaq SmallCap
Market or in  privately-negotiated  transactions  and have agreed to prepare and
file such  amendments and  supplements to the  registration  statement as may be
necessary to keep the registration  statement effective until the earlier of (i)
_______, 2002, (ii) the date on which all the shares of common stock may be sold
under  SEC  Rule  144(k)  (assuming  exercise  of all  applicable  warrants  and
conversion of all applicable debentures), or (iii) the date on which the selling
stockholders have sold all of the shares of common stock.

                                                          Securities Owned
                    Securities Owned Prior to Offering     After Offering
                                             Shares of
                                              Common    Number of  Percent
                     Shares of  Percent of     Stock    Shares of     of
Name of Selling       Common      Common      Offered   Common     Common
Stockholder            Stock       Stock      Hereby      Stock      Stock

Donald G. Drapkin     737,391(1)   9.97        737,391      0           *


Gabriel M. Cerrone    271,500(2)   3.95      210,000     61,500         *


Fahnestock & Co.,      52,500(3)     *        52,500        0           *
Inc.

Howard Gittis         509,804(4)   7.15      479,304     30,500         *


Lenore Katz            73,740(5)   1.10       73,740        0           *


Samuel Krieger          6,250(6)     *         6,250        0           *


Ronald Nussbaum         6,250(7)     *         6,250        0           *

                                       12


J. Jay Lobell         147,478(8)       2.17     147,478       0         *


Frank J. Loccisano    120,609(9)      1.78     110,609     10,000       *
and MaryAnne
Loccisano

Alfons Melohn         516,174(10)     7.20     516,174       0          *

Open-i Media, Inc.    125,000         1.88     125,000       0          *

Midnight Magic        213,478(11)     3.14     147,478      66,000      *
Investments
- -------------------
*  Less than one percent

(1)        Consists of 389,565 shares of common stock  issuable upon  conversion
           of  convertible  debentures  and 347,  826  shares  of  common  stock
           issuable upon exercise of warrants.

(2)        Consists of 210,000  shares of common stock issuable upon exercise of
           warrants.

(3)        Consists of 52,500  shares of common stock  issuable upon exercise of
           warrants.

(4)        Consists of 253,217 shares of common stock  issuable upon  conversion
           of convertible debentures and 226,087 shares of common stock issuable
           upon exercise of warrants.

(5)        Consists of 38,957 shares of common stock issuable upon conversion of
           convertible  debentures  and  34,783  shares  of  common  stock  upon
           exercise of warrants.

(6)        Consists of 6,250 shares of common stock  issuable  upon  exercise of
           warrants.

(7)        Consists of 6,250 shares of common stock  issuable  upon  issuance of
           warrants.

(8)        Consists of 77,913  shares of common stock  issuable upon exercise of
           convertible  debentures  and 69,565  shares of common stock  issuable
           upon exercise of warrants.

(9)        Consists of 58,435 shares of common stock issuable upon conversion of
           convertible  debentures  and 52,174  shares of common stock  issuable
           upon exercise of warrants.

(10)       Consists of 272,696 shares of common stock  issuable upon  conversion
           of convertible debentures and 243,478 shares of common stock issuable
           upon exercise of warrants.

(11)       Consists of 77,913 shares of common stock issuable upon conversion of
           convertible  debentures  and 69,565  shares of common stock  issuable
           upon exercise of warrants.

                                       13


      The  information  provided in the table above with  respect to the selling
stockholders has been obtained from such selling stockholders.

      Except as otherwise disclosed above or in documents incorporated herein by
reference,  the selling  stockholders,  except for Open-i  Media,  Inc. have not
within  the  past  three  years  had any  position,  office  or  other  material
relationship with us or any of our predecessors or affiliates.  In October 1999,
we  entered  into  an  agreement  with  Open-i  Media  for the  development  and
acquisition of the source code for a  client/server  chat and instant  messaging
internet application.  According to the agreement, as development milestones are
reached,  we will pay Open-i Media a combination  of $200,000 and 125,000 shares
of common stock.  In March 2000, we entered into an  additional  agreement  with
Open-i Media for  development and  consultation.  We will pay Open-i $280,000 in
cash and shares of common stock  against  certain  development  milestones to be
achieved in 2000. Because the selling  stockholders may sell all or some portion
of the  shares of common  stock  beneficially  owned by them,  only an  estimate
(assuming the selling stockholders sell all of the shares offered hereby) can be
given as to the number of shares of common stock that will be beneficially owned
by the  selling  stockholders  after this  offering.  In  addition,  the selling
stockholders may have sold,  transferred or otherwise  disposed of, or may sell,
transfer  or  otherwise  dispose  of, at any time or from time to time since the
dates on which they provided the information  regarding the shares  beneficially
owned by them,  all or a portion  of the  shares  beneficially  owned by them in
transactions exempt from the registration requirements of the Securities Act.




                                       14





                              PLAN OF DISTRIBUTION

      This  prospectus  covers  the sale of shares of common  stock from time to
time  by  the  selling  stockholders  named  in the  table  below.  The  selling
stockholder will act independently of us in making decisions with respect to the
timing,  manner  and size of each  sale.  The  sales  may be made on one or more
exchanges or in the over-the-counter market or otherwise, at prices and at terms
then  prevailing or at prices  related to the then current  market price,  or in
negotiated transactions. The selling stockholder may effect such transactions by
selling the shares to or through  broker-dealers.  The shares may be sold by one
or more of, or a combination of, the following:

o    a block trade in which the  broker-dealer  so engaged  will attempt to sell
     the shares as agent but may  position  and resell a portion of the block as
     principal to facilitate the transaction;

o    purchases by a broker-dealer as principal and resale by such  broker-dealer
     for its account pursuant to this prospectus;

o    an exchange distribution in accordance with the rules of such exchange;

o    ordinary  brokerage  transactions  and  transactions  in which  the  broker
     solicits purchasers; and

o    in privately negotiated transactions.

      To the extent  required,  this  prospectus may be amended or  supplemented
from time to time to  describe a specific  plan of  distribution.  In  effecting
sales,  broker-dealers  engaged by the selling stockholder may arrange for other
broker-dealers to participate in the resales.

      The  selling   stockholder  may  enter  into  hedging   transactions  with
broker-dealers in connection with  distributions of the shares or otherwise.  In
such transactions, broker-dealers may engage in short sales of the shares in the
course of hedging the positions  they assume with the selling  stockholder.  The
selling stockholder also may sell shares short and redeliver the shares to close
out such short positions. The selling stockholder may enter into option or other
transactions with broker-dealers which require the delivery to the broker-dealer
of the shares.  The  broker-dealer  may then resell or otherwise  transfer  such
shares pursuant to this prospectus.

      The  selling  stockholders  also  may  loan  or  pledge  the  shares  to a
broker-dealer.  The  broker-dealer  may sell the  shares  so  loaned,  or upon a
default  the  broker-dealer  may  sell  the  pledged  shares  pursuant  to  this
prospectus.  Broker-dealers  or agents may receive  compensation  in the form of
commissions,   discounts   or   concessions   from  the   selling   stockholder.
Broker-dealers  or agents may also receive  compensation  from the purchasers of
the  shares for whom they act as agents or to whom they sell as  principals,  or
both.  Compensation  as to a  particular  broker-dealer  might be in  excess  of
customary commissions and will be in amounts to be negotiated in connection with
the sale. Broker-dealers or agents and any other participating broker-dealers or
the selling  stockholders may be deemed to be "underwriters"  within the meaning
of Section 2(11) of the Securities  Act in connection  with sales of the shares.


                                       15


Accordingly,  any such commission,  discount or concession  received by them and
any  profit on the resale of the  shares  purchased  by them may be deemed to be
underwriting  discounts or  commissions  under the Securities  Act.  Because the
selling  stockholders may be deemed to be  "underwriters"  within the meaning of
Section 2(11) of the Securities Act, the selling stockholders will be subject to
the prospectus  delivery  requirements of the Securities  Act. In addition,  any
securities  covered by this  prospectus  which qualify for sale pursuant to Rule
144 promulgated  under the Securities Act may be sold under Rule 144 rather than
pursuant to this prospectus.  The selling stockholders have advised us that they
have not entered into any agreements,  understandings  or arrangements  with any
underwriters or broker-dealers regarding the sale of their securities.  There is
no underwriter  or  coordinating  broker acting in connection  with the proposed
sale of shares by the selling stockholders.

      The shares will be sold only  through  registered  or licensed  brokers or
dealers if required under  applicable  state  securities  laws. In addition,  in
certain  states the shares may not be sold unless they have been  registered  or
qualified for sale in the applicable state or an exemption from the registration
or qualification requirement is available and is complied with.

      Under applicable rules and regulations  under the Exchange Act, any person
engaged  in the  distribution  of the shares  may not  simultaneously  engage in
market  making  activities  with respect to our common stock for a period of two
business days prior to the commencement of such distribution.  In addition,  the
selling  stockholders  will be subject to applicable  provisions of the Exchange
Act and the associated rules and regulations  under the Exchange Act,  including
Regulation  M, which  provisions  may limit the timing of purchases and sales of
shares of our common stock by the selling  stockholders.  We will make copies of
this prospectus  available to the selling stockholders and have informed them of
the need for delivery of copies of this  prospectus to purchasers at or prior to
the time of any sale of the shares.

      We will file a supplement  to this  prospectus,  if required,  pursuant to
Rule  424(b)  under  the  Securities  Act upon  being  notified  by the  selling
stockholders  that  any  material  arrangement  has  been  entered  into  with a
broker-dealer  for the sale of shares through a block trade,  special  offering,
exchange  distribution  or secondary  distribution  or a purchase by a broker or
dealer. Such supplement will disclose:

o    the   name   of  the   selling   stockholder   and  of  the   participating
     broker-dealer(s);

o    the number of shares involved;

o    the price at which such shares were sold;

o    the  commissions   paid  or  discounts  or  concessions   allowed  to  such
     broker-dealer(s), where applicable;

o    that such  broker-dealer(s) did not conduct any investigation to verify the
     information set out or incorporated by reference in this prospectus; and

o    other facts material to the transaction.

                                       16


      We will  bear  all  costs,  expenses  and  fees  in  connection  with  the
registration of the shares.  The selling  stockholders will bear all commissions
and discounts,  if any,  attributable to the sales of the shares. We have agreed
to indemnify certain selling stockholders against certain liabilities, including
liabilities under the Securities Act of 1933, as amended, in connection with the
offering  of  the  shares  or to  contribute  to  payments  which  such  selling
stockholders  may  be  required  to  make  in  respect   thereof.   The  selling
stockholders may agree to indemnify  certain persons,  including  broker-dealers
and agents,  against certain  liabilities in connection with the offering of the
shares, including liabilities arising under the Securities Act.

                                       17


                                  LEGAL MATTERS

      The validity of the shares of common stock  offered  hereby will be passed
upon for Siga by Orrick, Herrington & Sutcliffe LLP.

                                     EXPERTS

      The financial  statements  incorporated in this prospectus by reference to
the Annual Report on Form 10-KSB of Siga  Technologies,  Inc. for the year ended
December  31,  1999 have  been so  incorporated  in  reliance  on the  report of
PricewaterhouseCoopers  LLP, independent accountants,  given on the authority of
said firm as experts in auditing and accounting.


                                       18


                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

              ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

      The  following  table sets forth the  estimated  costs and expenses of the
sale and distribution of the securities being registered, all of which are being
borne by us.

                                                     Amount

      Securities and Exchange Commission filing fee. $3,112
      Printing expenses.............................  2,000
      Legal Fees and Expenses....................... 10,000
      Accounting Fees and Expenses..................  5,000
      Miscellaneous.................................  3,888
                                                     -----------
          Total..................................... $24,000
                                                     =======

      All of the amounts shown are  estimates  except for the fee payable to the
Securities and Exchange Commission.

ITEM 15.   INDEMNIFICATION OF DIRECTORS AND OFFICERS

      Section  145 of the  Delaware  General  Corporation  Law  provides  that a
corporation may indemnify directors and officers, as well as other employees and
individuals,  against expenses (including attorneys' fees), judgments, fines and
amounts paid in settlement  actually and reasonably  incurred by any such person
in  connection  with any  threatened,  pending or  completed  actions,  suits or
proceedings  in which such person is made a party by reason of such person being
or having been a director,  officer,  employee or agent to the  Registrant.  The
Delaware  General  Corporation Law provides that Section 145 is not exclusive of
other rights to which those seeking  indemnification  may be entitled  under any
bylaw, agreement,  vote of stockholders or disinterested directors or otherwise.
Article IX of the Registrant's  Certificate of Incorporation  and Article VII of
the Registrant's  Bylaws provides for  indemnification  by the Registrant of its
directors and officers to the fullest extent  permitted by the Delaware  General
Corporation Law.

      Section  102(b)(7)  of the  Delaware  General  Corporation  Law  permits a
corporation to provide in its  certificate of  incorporation  that a director of
the  corporation  shall  not be  personally  liable  to the  corporation  or its
stockholders  for monetary  damages for breach of fiduciary  duty as a director,
except for liability (i) for any breach of the director's duty of loyalty to the
corporation or its stockholders, (ii) for acts or omissions not in good faith or
which involve  intentional  misconduct or a knowing  violation of law, (iii) for
unlawful  payments of dividends or unlawful  stock  repurchases,  redemptions or
other distributions, or (iv) for any transaction from which the director derived
an improper  personal  benefit.  The  Registrant's  Certificate of Incorporation
provides for such limitation of liability.

                                      II-1


ITEM 16.   EXHIBITS

      The  following  is a list of exhibits  filed as part of this  registration
statement.

           Exhibit
           Number    Description and Method of Filing
           ---------      ----------------------------------------
             3.1     Restated Certificate of Incorporation of the Registrant

             5       Opinion of Orrick, Herrington & Sutcliffe LLP

             23.1    Consent of Orrick,  Herrington & Sutcliffe  LLP
                     (included in the opinion filed as Exhibit 5)

             23.2    Consent of PricewaterhouseCoopers LLP

             24      Power of Attorney (See Page II-4)


ITEM 17. UNDERTAKINGS

   The undersigned registrant hereby undertakes:

(1) to file,  during  any  period in which  offers or sale;  are being  made,  a
post-effective amendment to this registration statement:

     (i)  to  include  any  prospectus  required  by  Section  10(a)(3)  of  the
          Securities Act of 1933;

     (ii) to reflect in the  prospectus  any facts or events  arising  after the
          effective  date of the  registration  statement  (or the  most  recent
          post-effective  amendment  thereof)  which,  individually  or  in  the
          aggregate, represent a fundamental change in the information set forth
          in the  registration  statement.  Notwithstanding  the foregoing,  any
          increase  or decrease  in volume of  securities  offered (if the total
          dollar  value of  securities  offered  would not exceed that which was
          registered)  and  any  deviation  from  the  low  or  high  end of the
          estimated  maximum  offering  range  may be  reflected  in the form of
          prospectus  filed with the  Commission  pursuant to Rule 424(b) if, in
          the aggregate,  the changes in volume and price represent no more than
          a 20% change in the maximum aggregate  offering price set forth in the
          "Calculation of Registration Fee" table in the effective  registration
          statement.

     (iii)to  include  any  material  information  with  respect  to the plan of
          distribution not previously disclosed in the registration statement or
          any material change to such information in the registration statement;

      provided,  however,  that paragraphs (1)(i) and (1)(ii) above do not apply
      if the registration statement is on Form S-3, and the information required
      to be,  included in a  post-effective  amendment  by those  paragraphs  is
      contained in periodic reports filed by the registrant  pursuant to Section
      13 or  Section  15(d)  of the  Securities  Exchange  Act of 1934  that are
      incorporated by reference in the registration statement.

                                      II-2


(2) That, for the purpose of determining  any liability under the Securities Act
of  1933,  each  such  post-effective  amendment  shall  be  deemed  to be a new
registration  statement  relating to the  securities  offered  therein,  and the
offering of such  securities  at the time shall be deemed to be the initial bona
fide offering thereof.

(3) To remove from  registration by means of a  post-effective  amendment any of
the securities  being  registered  which remain unsold at the termination of the
offering.

      The  undersigned  registrant  hereby  undertakes  that,  for  purposes  of
determining  any liability  under the Securities Act of 1933, each filing of the
registrant's  annual  report  pursuant to Section  13(a) or Section 15(d) of the
Securities  Exchange  Act of 1934  (and,  where  applicable,  each  filing of an
employee  benefit  plan's  annual  report  pursuant  to  Section  15(d)  of  the
Securities  Exchange  Act of 1934)  that is  incorporated  by  reference  in the
registration  statement shall be deemed to be a new registration relating to the
securities  offered  herein,  and the offering of such  securities  at that time
shall be deemed to be the initial bona fide offering thereof.

      The  undersigned  registrant  hereby  undertakes to deliver or cause to be
delivered with the prospectus,  to each person to whom the prospectus is sent or
given,  the latest annual report,  to security  holders that is  incorporated by
reference  in  the  prospectus  and  furnished   pursuant  to  and  meeting  the
requirements  of Rule 14a-3 or Rule 14c-3 under the  Securities  Exchange Act of
1934;  and,  where  interim  financial  information  required to be presented by
Article 3 of Regulation S-X is not set forth in the prospectus,  to deliver,  or
cause to be  delivered to each person to whom the  prospectus  is sent or given,
the latest  quarterly  report that is specifically  incorporated by reference in
the prospectus to provide such interim financial information.

      Insofar as  indemnification  for liabilities  arising under the Securities
Act of 1933 may be permitted to directors,  officers and controlling  persons of
the  registrant  pursuant  to  the  foregoing  provisions,   or  otherwise,  the
registrant  has been advised that in the opinion of the  Securities and Exchange
Commission such indemnification is against public policy as expressed in the Act
and is, therefore,  unenforceable. In the event that a claim for indemnification
against  such  liabilities  (other than  payment by the  registrant  of expenses
incurred or paid by a director,  officer or controlling person of the registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director,  officer or controlling person in connection with the securities being
registered, the registrant will, unless in the opinion of its counsel the matter
has been  settled by  controlling  precedent,  submit to a court of  appropriate
jurisdiction the question whether such indemnification by the final adjudication
of such issue.


                                      II-3


                                   SIGNATURES

   Pursuant  to  the   requirements   of  the  Securities  Act  of  1933,   Siga
Technologies,  Inc.  certifies that it has reasonable grounds to believe that it
meets all of the  requirements  for filing on Form S-3 and has duly  caused this
registration statement to be signed on its behalf by the undersigned,  thereunto
duly authorized, in the City of New York, New York on May 9, 2000.

                                    Siga Technologies, Inc.

                                    By: /s/ Joshua D. Schein
                                       -----------------------
                                    Joshua D. Schein, Ph.D.
                                    Chief Executive Officer

KNOW ALL PERSONS BY THESE  PRESENTS,  that the persons whose  signatures  appear
below each  severally  constitutes  and appoints  Joshua D. Schein and Judson A.
Cooper, and each of them, as true and lawful  attorneys-in-fact and agents, with
full powers of substitution  and  resubstitution,  for them in their name, place
and stead, in any and all capacities,  to sign any and all amendments (including
pre-effective and post-effective  amendments) to this registration statement and
to sign any registration statement (and any post-effective  amendments) relating
to the same offering as this registration statement that is to be effective upon
filing pursuant to Rule 462(b) under the Securities Act of 1933, and to file the
same, with all exhibits,  and other documents in connection therewith,  with the
Securities and Exchange  Commission,  granting unto said  attorneys-in-fact  and
agents,  and each of them,  full power and  authority to do and perform each and
every  act and  thing  requisite  and  necessary  to be done  in and  about  the
premises,  as fully to all  intents  and  purposes  as they might or could do in
person,  hereby  ratifying and confirming all which said  attorneys-in-fact  and
agents, or any of them, or their substitute or substitutes,  may lawfully do, or
cause to be done by virtue hereof.

      Pursuant to the  requirements  of the  Securities Act of 1933, as amended,
this  registration  statement has been signed below by the following  persons in
the capacities and on the dates indicated.

        Signature             Title of Capacities         Date

   /s/ Joshua D. Schein      Chief Executive           May 9, 2000,
- ------------------------
Joshua D. Schein, Ph.D.        Officer,
                               Secretary and
                               Director

   /s/ Judsen A. Cooper      Chairman of the Board     May 9, 2000,
- ------------------------     and Executive Vice
Judson A. Cooper             President


   /s/ Thomas Konatich       Chief Financial           May 9, 2000,
- ------------------------     Officer
Thomas Konatich

   /s/ Jeffrey Rubin            Director               May 9, 2000,
- ----------------------
Jeffrey Rubin

                                Director
- ----------------
Scott Eagle

   /s/ Thomas N. Lanier         Director               May 9, 2000,
- ------------------------
Thomas N. Lanier


                                      II-4

                                 EXHIBIT INDEX

      Exhibit
       Number
        3.1    Restated Certificate of Incorporation of the Registrant

          5    Opinion of Orrick, Herrington & Sutcliffe LLP

        23.1   Consent of Orrick, Herrington & Sutcliffe LLP (included in the
               opinion filed as Exhibit 5)

        23.2   Consent of PricewaterhouseCoopers LLP

         24    Power of Attorney (See Page II-4)

- -------------------------------------------------------------------------------
                                    RESTATED

                          CERTIFICATE OF INCORPORATION

                                       OF

                             SIGA TECHNOLOGIES, INC.
                             A Delaware Corporation

     Siga  Technologies,  Inc. a corporation  organized  and existing  under the
General Corporation Law of the State of Delaware, DOES HEREBY CERTIFY:

     FIRST: The name of the Corporation is Siga Technologies,  Inc. and the name
under   which   the   Corporation   was   originally   incorporated   was   Siga
Pharmaceuticals,  Inc.  The  date  of  filing  of its  original  Certificate  of
Incorporation  with the Secretary of State of the State of Delaware was December
28, 1995.

     SECOND: The Restated Certificate of Incorporation of Siga  Pharmaceuticals,
Inc. in the form attached  hereto as Exhibit A restates and  integrates but does
not further amend the Certificate of Incorporation of Siga  Technologies,  Inc.,
and  there  is no  discrepancy  between  the  provisions  of  the  Corporation's
Certificate  of  Incorporation  as heretofore  amended or  supplemented  and the
provisions of the Restated  Certificate of Incorporation  attached hereto, which
has been duly adopted in  accordance  with the  provisions of Section 245 of the
General Corporation Law of the State of Delaware by the unanimous consent of the
directors of the Corporation dated April 25th, 2000.

     THIRD:  The Restated  Certificate of Incorporation so adopted reads in full
as set forth in  Exhibit  A  attached  hereto  and  incorporated  herein by this
reference.

     IN WITNESS WHEREOF,  I have hereunto set my hand as Chief Executive Officer
of Siga Technologies, Inc. and hereby affirm under penalties of perjury that the
foregoing  is my act  and  deed  and the  facts  herein  stated  are  true,  and
accordingly have hereunto set forth my hand this 25th day of April, 2000

                                    /s/ Joshua D. Schein
                                    Joshua D. Schein
                                    Chief Executive Officer


                                     1


                                    RESTATED

                          CERTIFICATE OF INCORPORATION

                                       OF

                             SIGA TECHNOLOGIES, INC.

     FIRST:  The  name  of the  Corporation  is  Siga  Technologies,  Inc.  (the
"Corporation").

     SECOND: The address of the Corporation's  registered office in the State of
Delaware is 1013 Centre Road,  Wilmington,  County of New Castle 19805. The name
of the registered agent of the Corporation at such address is The  Prentice-Hall
Corporation System, Inc.

     THIRD:  The  purpose of the  Corporation  is to engage in any lawful act or
activity for which a Corporation may be organized under the General  Corporation
Law of Delaware.

     FOURTH: The total number of shares of stock which the Corporation shall
have  authority to issue is sixty million  (60,000,000),  of which fifty million
(50,000,000)  shares of the par  value of One  Hundredth  of One Cent  ($0.0001)
each,  amounting in the aggregate to Five Thousand  Dollars  ($5,000),  shall be
Common Stock, and of which ten million  (10,000,000)  shares of the par value of
One  Hundredth of One Cent  ($0.0001)  each,  amounting in the  aggregate to One
Thousand Dollars ($1,000), shall be Preferred Stock.

     The Board of Directors  shall have the authority to fix by  Resolution  the
voting  powers (full,  limited,  multiple,  fractional  or none),  designations,
preferences,  qualifications,  privileges,  limitations,  restrictions, options,
conversion rights and other special or relative rights of the Preferred Stock or
any class or series thereof prior to or  concurrently  with the issuance of such
shares.

     There shall be no cumulative voting rights for the Common Stock.

     The holders of the Common Stock and the  Preferred  Stock shall be entitled
to  dividends,  when,  as and if  declared  by the  Board  of  Directors  of the
Corporation,  payable  at such  time or times  as the  Board  of  Directors  may
determine.

     Subject to the  determination  of the Board of Directors with regard to the
Preferred Stock, in the event of any  liquidation,  dissolution or winding up of
the affairs of the Corporation,  whether voluntary or involuntary, all remaining
assets  and  funds  of  the  Corporation   available  for  distribution  to  its
stockholders  shall be  distributed  in equal  amounts  per  share  and  without
preference or priority of one class of common stock over the other.

     Any action may be taken by the  stockholders  of the  Corporation  by their
written consent without a stockholders' meeting.

     No stockholder of this Corporation shall by reason of his holding shares
of any class have any preemptive or preferential  right to purchase or subscribe
to any  shares  of any  class  of  this  Corporation,  now  or  hereafter  to be
authorized,  or any notes,  debentures,  bonds, or other securities  convertible
into or carrying  options or warrants  to purchase  shares of any class,  now or





hereafter to be authorized,  whether or not the issuance of any such shares,  or
such notes,  debentures,  bonds or other securities,  would adversely affect the
dividend or voting rights of such  stockholder,  other than such rights, if any,
as the board of directors, in its discretion from time to time may grant, and at
such price as the Board of Directors in its discretion may fix; and the Board of
Directors  may  issue  shares of any class of this  Corporation,  or any  notes,
debentures,  bonds, or other securities  convertible into or carrying options or
warrants to purchase  shares of any class,  without  offering any such shares of
any  class,  either in whole or in part,  to the  existing  stockholders  of any
class.

     FIFTH:  The number of  directors of the  Corporation  shall be such as from
time to time shall be fixed by, or in the manner provided in, the by-laws of the
Corporation.  No election of directors  need be by ballot  unless the by-laws so
provide.

     SIXTH:  The  Corporation  hereby  expressly  elects not to be  governed  by
Section 203 of the General Corporation Law of Delaware.

     SEVENTH:  No director of the Corporation  shall be personally liable to the
Corporation  or its  stockholders  for monetary  damages for breach of fiduciary
duty as a director,  provided,  however, that this provision shall not eliminate
or limit the liability of a director (i) for any breach of the  director's  duty
of loyalty to the  Corporation or its  stockholders,  (ii) for acts or omissions
not in good faith or which involve intentional misconduct or a knowing violation
of law, (iii) under Section 174 of the General  Corporation Law of Delaware,  or
(iv) from any transaction from which the director  derived an improper  personal
benefit.

     EIGHTH: The Corporation shall indemnify, in accordance with and to the full
extent now or hereafter permitted by law, any person who was or is a party or is
threatened to be made a party to any  threatened,  pending or completed  action,
suit or proceeding,  whether civil,  criminal,  administrative  or investigative
(including,   without  limitation,   an  action  by  or  in  the  right  of  the
Corporation),  by reason of his acting as a director of the Corporation (and the
Corporation, in the discretion of the Board, may so indemnify a person by reason
of the fact that he is or was an officer or employee of the Corporation or is or
was serving at the request of the  Corporation  in any other  capacity for or on
behalf of the  Corporation)  against  any  liability  or  expense  actually  and
reasonably incurred by such person in respect thereof; provided,  however, that,
the  Corporation  shall not be obligated  to indemnify  any such person (i) with
respect to proceedings,  claims or actions  initiated or brought  voluntarily by
such  person  and  not by way of  defense,  or  (ii)  for  any  amounts  paid in
settlement  of an action  effected  without  the prior  written  consent  of the
Corporation to such  settlement.  Such  indemnification  is not exclusive of any
other right to indemnification provided by law, agreement or otherwise.

      NINTH: No amendment to or repeal of Article Seven or Article Eight of this
Certificate of Incorporation  shall apply to or have any effect on the rights of
any individual referred to in Article Seven or Article Eight for or with respect
to acts or omissions of such  individual  occurring  prior to such  amendment or
repeal.

      TENTH:  Whenever a  compromise  or  arrangement  is proposed  between this
Corporation  and  its  creditors  or any  class  of  them  and/or  between  this
Corporation  and its  stockholders  or any



class of them, any court of equitable  jurisdiction within the State of Delaware
may, on the application in a summary way of this  Corporation or of any creditor
or  stockholder  thereof or on the  application  of any  receiver  or  receivers
appointed for this Corporation under the provisions of Section 291 of Title 8 of
the Delaware Code or on the  application  of trustees in  dissolution  or of any
receiver or receivers  appointed for this  Corporation  under the  provisions of
Section 279 of Title 8 of the Delaware Code, order a meeting of the creditors or
class of creditors,  and/or of the stockholders or class of stockholders of this
Corporation, as the case may be, to be summoned in such manner as the said court
directs.  If a majority  in number  representing  three-fourths  in value of the
creditors  or  class  of  creditors,  and/or  of the  stockholders  or  class of
stockholders of this Corporation, as the case may be, agree to any compromise or
arrangement and to any reorganization of this Corporation as consequence of such
compromise  or  arrangement,  the said  compromise or  arrangement  and the said
reorganization  shall, if sanctioned by the court to which the said  application
has been made, be binding on all the creditors or class of creditors,  and/or on
all the stockholders or class of stockholders,  of this Corporation, as the case
may be, and also on this Corporation.

     ELEVENTH:  The Board of  Directors  shall have power  without the assent or
vote of the stockholders to make,  alter,  amend,  change,  add to or repeal the
by-laws of the Corporation.

     TWELFTH: The Corporation shall have perpetual existence.

     IN WITNESS  WHEREOF,  I have  hereunto  set my hand this 24th day of April,
2000.

                                    SIGA TECHNOLOGIES, INC.


                                    By:   /s/Joshua D. Schein
                                        ------------------------
                                       Name:Joshua D. Schein
                                       Title:  Chief Executive
                                       Officer
                                   May 4, 2000

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


           Re:  Siga Technologies, Inc.
                Registration Statement on Form S-3

           We have  acted as  counsel  to Siga  Technologies,  Inc.,  a Delaware
corporation (the "Company"),  in connection with the preparation and filing of a
Registration  Statement  on Form S-3  (the  "Registration  Statement")  with the
Securities and Exchange  Commission under the Securities Act of 1933, as amended
(the "Act").  The Registration  Statement relates to the sale by certain selling
stockholders  of the Company of up to 2,833,391  shares of the Company's  Common
Stock (the  "Shares").  This opinion is being  furnished in accordance  with the
requirements of item 16 of Form S-3 and Item 601(b)(5)(i) of Regulation S-K.

           We have  reviewed the Company's  charter  documents and the corporate
proceedings  taken by the Company in connection with the issuance of the Shares.
Based on such  review,  we are of the  opinion  that the  Shares  have been duly
authorized,  and if,  as and  when  sold in  accordance  with  the  Registration
Statement and the related  prospectus (as amended and  supplemented  through the
date of sale) will be legally issued, fully paid and nonassessable.

           We consent to the filing of this opinion letter as Exhibit 5.1 to the
Registration  Statement  and to the  reference  to this firm  under the  caption
"Legal Matters" in the prospectus which is part of the  Registration  Statement.
In giving this consent,  we do not thereby admit that we are within the category
of persons whose  consent is required  under Section 7 of the Act, the rules and
regulations of the Securities and Exchange Commission promulgated thereunder, or
Item 509 of Regulation S-K. This opinion letter is rendered as of the date first
written  above  and  we  disclaim  any   obligation  to  advise  you  of  facts,
circumstances,  events or  developments  which  hereafter  may be brought to our
attention and which may alter,  affect or modify the opinion  expressed  herein.
Our opinion is expressly limited to the matters set forth above and we render no
opinion,  whether by implication or otherwise,  as to any other matters relating
to the Company or the Shares.

                                Very truly yours,

                               /s/ Orrick, Herrington & Sutcliffe LLP


                      CONSENT OF INDEPENDENT ACCOUNTANTS

We  hereby  consent  to the  incorporation  by  reference  in this  Registration
Statement on Form S-3 of our report dated February 18, 2000,  except for Note 13
which is as of March 30,  2000,  relating  to the  financial  statements,  which
appear in Siga Technologies,  Inc.'s Annual Report on Form 10-KSB/A for the year
ended  December  31,  1999.  We also  consent to the  reference  to us under the
heading "Experts" in such Registration Statement.

/s/ PricewaterhouseCoopers LLP

New York, NY
May 9, 2000