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  <xsd:element id="siga_ContractValueDetailOfOptionExercisableProductionActivities" name="ContractValueDetailOfOptionExercisableProductionActivities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ContractValueOfDevelopmentAndSupportActivities" name="ContractValueOfDevelopmentAndSupportActivities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ContractValueOptionFDAApproval" name="ContractValueOptionFDAApproval" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ContractValueofManufacturingandDeliveryActivities" name="ContractValueofManufacturingandDeliveryActivities" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ContractValueofVariousOptions" name="ContractValueofVariousOptions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_DebtInstrumentCapacitybySpecificPurposeAxis" name="DebtInstrumentCapacitybySpecificPurposeAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_DebtInstrumentCapacitybySpecificPurposeDomain" name="DebtInstrumentCapacitybySpecificPurposeDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_DocumentAndEntityInformationAbstract" name="DocumentAndEntityInformationAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_EquityRightsMember" name="EquityRightsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_FairValueMeasurementsAbstract" name="FairValueMeasurementsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_FinalOrderAndJudgment" name="FinalOrderAndJudgment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="siga_FinalOrderAndJudgmentPostJudgmentInterest" name="FinalOrderAndJudgmentPostJudgmentInterest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="siga_Finalorderandjudgmentplusinterest" name="Finalorderandjudgmentplusinterest" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="siga_FreeRentPeriod" name="FreeRentPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_GovernmentContractNumberOfCoursesPurchasedUnderModifiedContract" name="GovernmentContractNumberOfCoursesPurchasedUnderModifiedContract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_GovernmentContractNumberofFreeCourses" name="GovernmentContractNumberofFreeCourses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_GovernmentContractTotalNumberofCoursesRequiredtoBeDelivered" name="GovernmentContractTotalNumberofCoursesRequiredtoBeDelivered" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_GovernmentContractValueOfAward1" name="GovernmentContractValueOfAward1" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_HoldbackamountpendingFDAapproval" name="HoldbackamountpendingFDAapproval" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_IncreaseInFairValueOfWarrants" name="IncreaseInFairValueOfWarrants" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_IncreaseinpaymentsfordeliveryofcoursesofTPOXX" name="IncreaseinpaymentsfordeliveryofcoursesofTPOXX" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="siga_IncreasetoFundingofResearchandDevelopmentContract" name="IncreasetoFundingofResearchandDevelopmentContract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_InitialRentPeriod" name="InitialRentPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_InterestPaidonTermLoanFromRestrictedCash" name="InterestPaidonTermLoanFromRestrictedCash" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_InventoryAbstract" name="InventoryAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_InventoryWriteDowns" name="InventoryWriteDowns" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_LicenseAgreementLitigationMember" name="LicenseAgreementLitigationMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_LineofCreditFacilityAdditionalBorrowingCapacity" name="LineofCreditFacilityAdditionalBorrowingCapacity" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="siga_LineofCreditFacilityDebtDefaultIncreaseinInterestRate" name="LineofCreditFacilityDebtDefaultIncreaseinInterestRate" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_LineofCreditFacilityMinimumCashRequirement" name="LineofCreditFacilityMinimumCashRequirement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_LoanAgreementMember" name="LoanAgreementMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_MilestonePayment" name="MilestonePayment" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_MonthlyRentalPaymentsAfterFiveYears" name="MonthlyRentalPaymentsAfterFiveYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_MonthlyRentalPaymentsFirstFiveYears" name="MonthlyRentalPaymentsFirstFiveYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_NumberOfActiveGrants" name="NumberOfActiveGrants" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_NumberOfCoursesDeliveredAndAcceptedAtProvisionalDosageOnceDaily" name="NumberOfCoursesDeliveredAndAcceptedAtProvisionalDosageOnceDaily" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_NumberOfCoursesToBeDelivered1" name="NumberOfCoursesToBeDelivered1" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_NumberofCoursestobeDeliveredbyCompany" name="NumberofCoursestobeDeliveredbyCompany" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="instant" />
  <xsd:element id="siga_PatentPreparationFees" name="PatentPreparationFees" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_PaymentofInterestExpense" name="PaymentofInterestExpense" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_PaymentsRelatedtoLitigationMember" name="PaymentsRelatedtoLitigationMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_PotentialFutureAggregateResearchAndDevelopmentExpenses" name="PotentialFutureAggregateResearchAndDevelopmentExpenses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="siga_ProceedsFromAdvancePaymentsGovernmentContracts" name="ProceedsFromAdvancePaymentsGovernmentContracts" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ProceedsFromManufactureAndPhysicalDeliveryOfCoursesGovernmentContracts" name="ProceedsFromManufactureAndPhysicalDeliveryOfCoursesGovernmentContracts" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="siga_ProceedsFromPhysicalDeliveryOfCoursesGovernmentContracts" name="ProceedsFromPhysicalDeliveryOfCoursesGovernmentContracts" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ProcurementContractAndResearchAgreementsTextBlock" name="ProcurementContractAndResearchAgreementsTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_ProcurementContractAxis" name="ProcurementContractAxis" nillable="true" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_ProcurementContractDomain" name="ProcurementContractDomain" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_ProcurementContractLineItems" name="ProcurementContractLineItems" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_ProcurementContractTable" name="ProcurementContractTable" nillable="true" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_RecentAccountingPronouncementsAbstract" name="RecentAccountingPronouncementsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_Reducedholdbackamount" name="Reducedholdbackamount" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_RentPeriodAfterFirstFiveYears" name="RentPeriodAfterFirstFiveYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_ReorganizationPayments" name="ReorganizationPayments" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ReorganizationProfessionalFees" name="ReorganizationProfessionalFees" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ReorganizationTrusteefees" name="ReorganizationTrusteefees" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ReorganizationitemsTableTextBlock" name="ReorganizationitemsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_RepaymentofInterestsMember" name="RepaymentofInterestsMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_ResearchAndDevelopmentRevenue" name="ResearchAndDevelopmentRevenue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="siga_ResearchandDevelopmentRevenueLongtermContract" name="ResearchandDevelopmentRevenueLongtermContract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element id="siga_RestrictedStockUnits" name="RestrictedStockUnits" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_SeniorSecuredTermLoanMember" name="SeniorSecuredTermLoanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_StockIssuedDuringPeriodSharesRightsOffering" name="StockIssuedDuringPeriodSharesRightsOffering" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_SubscriptionRightMember" name="SubscriptionRightMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_USTreasuryRateMember" name="USTreasuryRateMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
</xsd:schema>