<SEC-DOCUMENT>0001140361-13-014184.txt : 20130327
<SEC-HEADER>0001140361-13-014184.hdr.sgml : 20130327
<ACCEPTANCE-DATETIME>20130327162820
ACCESSION NUMBER:		0001140361-13-014184
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20130322
FILED AS OF DATE:		20130327
DATE AS OF CHANGE:		20130327

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Benjamin Howard
		CENTRAL INDEX KEY:			0001393547

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-14656
		FILM NUMBER:		13720315

	MAIL ADDRESS:	
		STREET 1:		401 MARRETT ROAD
		CITY:			LEXINGTON
		STATE:			MA
		ZIP:			02421

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			REPLIGEN CORP
		CENTRAL INDEX KEY:			0000730272
		STANDARD INDUSTRIAL CLASSIFICATION:	BIOLOGICAL PRODUCTS (NO DIAGNOSTIC SUBSTANCES) [2836]
		IRS NUMBER:				042729386
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		41 SEYON STREET
		STREET 2:		BUILDING 1, SUITE 100
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02453
		BUSINESS PHONE:		7814499560

	MAIL ADDRESS:	
		STREET 1:		41 SEYON STREET
		STREET 2:		BUILDING 1, SUITE 100
		CITY:			WALTHAM
		STATE:			MA
		ZIP:			02453
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3
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<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2013-03-22</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000730272</issuerCik>
        <issuerName>REPLIGEN CORP</issuerName>
        <issuerTradingSymbol>RGEN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001393547</rptOwnerCik>
            <rptOwnerName>Benjamin Howard</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O REPLIGEN CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>41 SEYON ST, BLDG 1, STE 100</rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02453</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
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        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP Business Development</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>4.25</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2010-02-11</value>
            </exerciseDate>
            <expirationDate>
                <value>2019-02-11</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>100000</value>
                    <footnoteId id="F1"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>3.33</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2011-07-15</value>
            </exerciseDate>
            <expirationDate>
                <value>2020-07-15</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>25000</value>
                    <footnoteId id="F2"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>6.23</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2014-02-28</value>
            </exerciseDate>
            <expirationDate>
                <value>2023-02-28</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>40000</value>
                    <footnoteId id="F3"/>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">100,000 options were granted on 02/11/2009. 20,000 options vested on each of the following dates: 02/11/2010, 02/11/2011, 02/11/2012 and 02/11/2013. 20,000 options will vest on 02/11/2014.</footnote>
        <footnote id="F2">25,000 options were granted on 07/15/2010. 5,000 options vested on each of the following dates: 07/15/2011 and 07/15/2012. 5,000 options will vest on each of the following dates: 07/15/2013, 07/15/2014 and 07/15/2015.</footnote>
        <footnote id="F3">40,000 options were granted on 02/28/2013. 10,000 options will vest on each of the following dates: 02/28/2014, 02/28/2015, 02/28/2016 and 02/28/2017.</footnote>
    </footnotes>

    <remarks>Exhibit List

Exhibit 24  Power of Attorney</remarks>

    <ownerSignature>
        <signatureName>/s/ William J. Kelly (Attorney in Fact)</signatureName>
        <signatureDate>2013-03-27</signatureDate>
    </ownerSignature>
</ownershipDocument>
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<DOCUMENT>
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<DESCRIPTION>POWER OF ATTORNEY
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<div style="TEXT-INDENT: 0pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="center"><font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt; FONT-WEIGHT: bold"><font style="DISPLAY: inline; TEXT-DECORATION: underline">POWER OF ATTORNEY</font></font></div>

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<div style="TEXT-INDENT: 36pt; DISPLAY: block; MARGIN-LEFT: 0pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-FAMILY: Times New Roman; FONT-SIZE: 10pt">KNOW ALL MEN BY THESE PRESENTS, that the person whose signature appears below hereby constitutes and appoints Jonathan I. Lieber and William J. Kelly, and any one of them acting singly, the true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution, for the undersigned and in the undersigned&#8217;s name, place and stead, in any and all capacities (until revoked in writing) to sign any and all instruments, certificates and documents required to be executed on behalf of the undersigned as an individual or on behalf of the undersigned&#8217;s holding company, as the case may be, relating to securities, or transactions in securities, of Repligen Corporation, pursuant to sections 13 and 16 of the Securities Exchange Act of 1934, as amended (the &#8220;Exchange Act&#8221;), and any and all regulations promulgated thereunder, and to file the same, with all exhibits thereto, and any other documents in connection therewith, with the Securities and Exchange Commission, and with any other entity when and if such is mandated by the Exchange Act or by the By-laws of the National Association of Securities Dealers, granting unto said attorneys-in-fact and agents full power and authority to do and perform each and every act and thing requisite and necessary fully to all intents and purposes as the undersigned might or could do in person thereby ratifying and confirming all that said attorneys-in-fact and agents, or their substitute or substitutes, may lawfully do or cause to be done by virtue hereof.</font></div>

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