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        <link:definition xmlns="http://www.xbrl.org/2003/linkbase">035 - Disclosure - Note 9 - Subsequent Event (Details Textual)</link:definition>
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        <link:usedOn>link:definitionLink</link:usedOn>
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  <xsd:element id="bcrx_ReceivablesPayablesNetCurrent" name="ReceivablesPayablesNetCurrent" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="instant"/>
  <xsd:element id="bcrx_RenewablePeriodOfAgreement" name="RenewablePeriodOfAgreement" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyExpenseReversalOfExpense" name="RoyaltyExpenseReversalOfExpense" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyFinancingObligationInterestAccretion" name="RoyaltyFinancingObligationInterestAccretion" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_RoyaltyMonetizationMember" name="RoyaltyMonetizationMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyMonetizationTextBlock" name="RoyaltyMonetizationTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyPaymentsReceivableExpirationTermFromFirstCommercial" name="RoyaltyPaymentsReceivableExpirationTermFromFirstCommercial" nillable="true" substitutionGroup="xbrli:item" type="xbrli:durationItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInKeyTerritories" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInKeyTerritories" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInOtherMarkets" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfAnnualNetSalesInOtherMarkets" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfGlobalAnnualNetSales" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfGlobalAnnualNetSales" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyPurchaseAgreementRoyaltiesPercentageOfSublicenseRevenueInOtherMarkets" name="RoyaltyPurchaseAgreementRoyaltiesPercentageOfSublicenseRevenueInOtherMarkets" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_RoyaltyRateIfMaintainsSakigakeDesignation" name="RoyaltyRateIfMaintainsSakigakeDesignation" nillable="true" substitutionGroup="xbrli:item" type="num:percentItemType" xbrli:periodType="instant"/>
  <xsd:element abstract="true" id="bcrx_RoyaltyReceivableMember" name="RoyaltyReceivableMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_ScheduleOfReceivablesFromCollaborationsTableTextBlock" name="ScheduleOfReceivablesFromCollaborationsTableTextBlock" nillable="true" substitutionGroup="xbrli:item" type="nonnum:textBlockItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_SecuredCreditFacilityFirstTrancheMember" name="SecuredCreditFacilityFirstTrancheMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_SecuredCreditFacilitySecondTrancheMember" name="SecuredCreditFacilitySecondTrancheMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_SecuredCreditFacilityThirdTrancheMember" name="SecuredCreditFacilityThirdTrancheMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_SeniorCreditFacilityMember" name="SeniorCreditFacilityMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodAwardsAvailable" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodAwardsAvailable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_ShareBasedCompensationArrangementBySharebasedPaymentAwardMaximumNumberOfSharesPerEmployeeAmount" name="ShareBasedCompensationArrangementBySharebasedPaymentAwardMaximumNumberOfSharesPerEmployeeAmount" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:periodType="instant"/>
  <xsd:element id="bcrx_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsForfeituresInPeriodAwardsAvailable" name="SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsForfeituresInPeriodAwardsAvailable" nillable="true" substitutionGroup="xbrli:item" type="xbrli:sharesItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_ShionogiAndCoLtdMember" name="ShionogiAndCoLtdMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_TermALoanMember" name="TermALoanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_TermBLoanMember" name="TermBLoanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_TermCLoanMember" name="TermCLoanMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_TermLoanAAndBDrawnMember" name="TermLoanAAndBDrawnMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_TermLoanADrawnMember" name="TermLoanADrawnMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_TermLoansABAndCDrawnAndCureRightExercisedMember" name="TermLoansABAndCDrawnAndCureRightExercisedMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_TermLoansABAndCDrawnMember" name="TermLoansABAndCDrawnMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_ToriiPharmaceuticalCoMember" name="ToriiPharmaceuticalCoMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_TransactionCosts" name="TransactionCosts" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_UABMember" name="UABMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_USDepartmentOfHealthAndHumanServicesMember" name="USDepartmentOfHealthAndHumanServicesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element id="bcrx_UpfrontPaymentsReceivableAmount" name="UpfrontPaymentsReceivableAmount" nillable="true" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType" xbrli:balance="debit" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_Vest25PercentEachYearUntilFullyVestedMember" name="Vest25PercentEachYearUntilFullyVestedMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_VestUponSuccessfulCompletionOfSpecificDevelopmentMilestonesMember" name="VestUponSuccessfulCompletionOfSpecificDevelopmentMilestonesMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_WarrantsIssuedInPublicOfferingMember" name="WarrantsIssuedInPublicOfferingMember" nillable="true" substitutionGroup="xbrli:item" type="nonnum:domainItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-1-significant-accounting-policies-fair-value-of-the-companys-investments-by-type-details" name="statement-statement-note-1-significant-accounting-policies-fair-value-of-the-companys-investments-by-type-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-1-significant-accounting-policies-summary-of-inventories-details" name="statement-statement-note-1-significant-accounting-policies-summary-of-inventories-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-1-significant-accounting-policies-summary-of-receivables-details" name="statement-statement-note-1-significant-accounting-policies-summary-of-receivables-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-1-significant-accounting-policies-summary-of-revenues-details" name="statement-statement-note-1-significant-accounting-policies-summary-of-revenues-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-1-significant-accounting-policies-tables" name="statement-statement-note-1-significant-accounting-policies-tables" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-5-lease-obligations-and-other-contingencies-remaining-maturities-of-lease-liabilities-details" name="statement-statement-note-5-lease-obligations-and-other-contingencies-remaining-maturities-of-lease-liabilities-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-5-lease-obligations-and-other-contingencies-tables" name="statement-statement-note-5-lease-obligations-and-other-contingencies-tables" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-7-stockbased-compensation-stock-plan-activities-details" name="statement-statement-note-7-stockbased-compensation-stock-plan-activities-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-7-stockbased-compensation-tables" name="statement-statement-note-7-stockbased-compensation-tables" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-note-7-stockbased-compensation-weighted-average-assumptions-for-stock-option-awards-granted-to-employees-and-directors-under-the-plans-details" name="statement-statement-note-7-stockbased-compensation-weighted-average-assumptions-for-stock-option-awards-granted-to-employees-and-directors-under-the-plans-details" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
  <xsd:element abstract="true" id="bcrx_statement-statement-significant-accounting-policies-policies" name="statement-statement-significant-accounting-policies-policies" nillable="true" substitutionGroup="xbrli:item" type="xbrli:stringItemType" xbrli:periodType="duration"/>
</xsd:schema>
