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  <xsd:element id="siga_GovernmentContractNumberOfCoursesToBeDeliveredThreshold" name="GovernmentContractNumberOfCoursesToBeDeliveredThreshold" 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: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_InitialRentPeriod" name="InitialRentPeriod" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_LeasePropertyPricePerMonth1" name="LeasePropertyPricePerMonth1" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element abstract="true" id="siga_LicenseAgreementLitigationMember" name="LicenseAgreementLitigationMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_LitigationCostsAwardedPercentage" name="LitigationCostsAwardedPercentage" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" 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:periodType="duration" />
  <xsd:element id="siga_MonthlyRentalPaymentsFirstFiveYears" name="MonthlyRentalPaymentsFirstFiveYears" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_NetProfitMilestone" name="NetProfitMilestone" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="instant" />
  <xsd:element id="siga_NumberOfActiveContracts" name="NumberOfActiveContracts" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" 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_NumberOfCoursesToBeDelivered1" name="NumberOfCoursesToBeDelivered1" nillable="true" substitutionGroup="xbrli:item" type="xbrli:integerItemType" xbrli:periodType="duration" />
  <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_PaymentToPostCollateralForSuretyBond" name="PaymentToPostCollateralForSuretyBond" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant" />
  <xsd:element id="siga_PercentageOfNetProfitsFromSalesAfterNetProfitMilestoneResultingFromAwardDamages" name="PercentageOfNetProfitsFromSalesAfterNetProfitMilestoneResultingFromAwardDamages" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
  <xsd:element id="siga_PotentialFutureAggregateResearchAndDevelopmentExpenses" name="PotentialFutureAggregateResearchAndDevelopmentExpenses" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" 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_ProceedsFromIssuanceOfWarrantsAndOptions" name="ProceedsFromIssuanceOfWarrantsAndOptions" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration" />
  <xsd:element id="siga_ProceedsFromIssuanceOfWarrantsAndOptions1" name="ProceedsFromIssuanceOfWarrantsAndOptions1" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="instant" />
  <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_ReclassOfCommonStockWarrantLiabilityToAdditionalPaidInCapitalUponExercise" name="ReclassOfCommonStockWarrantLiabilityToAdditionalPaidInCapitalUponExercise" 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_ResearchAndDevelopmentRevenue" name="ResearchAndDevelopmentRevenue" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="credit" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_RevisedAdjustmentMember" name="RevisedAdjustmentMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration" />
  <xsd:element abstract="true" id="siga_RevisionOfConsolidatedFinancialStatementsAbstract" name="RevisionOfConsolidatedFinancialStatementsAbstract" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_ServiceAgreementTerm" name="ServiceAgreementTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_WarrantsContractrualTerm" name="WarrantsContractrualTerm" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration" />
  <xsd:element id="siga_WarrantsExercised" name="WarrantsExercised" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="instant" />
  <xsd:element id="siga_WarrantsExpired" name="WarrantsExpired" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="instant" />
  <xsd:element id="siga_WarrantsToPurchasePercentageOfShares" name="WarrantsToPurchasePercentageOfShares" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant" />
</xsd:schema>