<SEC-DOCUMENT>0001140361-14-041292.txt : 20141112
<SEC-HEADER>0001140361-14-041292.hdr.sgml : 20141111
<ACCEPTANCE-DATETIME>20141112155306
ACCESSION NUMBER:		0001140361-14-041292
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		2
CONFORMED PERIOD OF REPORT:	20141111
FILED AS OF DATE:		20141112
DATE AS OF CHANGE:		20141112

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

REPORTING-OWNER:	

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

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-14656
		FILM NUMBER:		141213821

	MAIL ADDRESS:	
		STREET 1:		401 MARRETT ROAD
		CITY:			LEXINGTON
		STATE:			MA
		ZIP:			02421
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-11-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <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>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP Business Development</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-11-11</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>30000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.56</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>43851</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">$23.56 is a weighted average price.  These shares were sold in multiple transactions at the prices ranging from $23.10 to $23.87, inclusive.  The reporting person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each seperate price within range.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Brian Salerno</signatureName>
        <signatureDate>2014-11-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
<DOCUMENT>
<TYPE>EX-24
<SEQUENCE>2
<FILENAME>poa_benjamin.htm
<TEXT>
<html>
<head>
    <title>Unassociated Document</title>



</head>
<body bgcolor="#ffffff">
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<div align="center"><font>POWER OF ATTORNEY</font></div>

<div><br>
</div>

<div align="left"><font>KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints Walter C. Herlihy, Jon Snodgres, and Brian Salerno, 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's name, place and stead, in any and all capacities (until revoked in writing) to execute for and on behalf of the undersigned, in any and all of the undersigned's capacities, any and all statements on Forms 3, 4 and 5 with respect to the undersigned's holdings of and transactions in securities issued by Repligen Corporation (the "Company") in accordance with Sections 16(a) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), 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 Financial Industry Regulatory Authority, 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>

<div><br>
</div>

<div align="left"><font>This Power of Attorney shall remain in full force and effect until the undersigned is no longer required to file Forms 3, 4 and 5 with respect to the undersigned's holdings of and transactions in securities issued by the Company, unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorney-in-fact.</font></div>

<div><br>
</div>

<div align="left"><font>IN WITNESS WHEREOF, this Power of Attorney has been signed as of November 12, 2014.</font></div>

<div><br>
</div>

<div align="left">
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<tr>
<td valign="top" width="50%"><font>&#160; </font></td>
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<div align="left"><font><font>/s/ Howard Benjamin</font></font></div>
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<td valign="top" width="10%"><font>&#160; </font></td>
</tr><tr>
<td valign="top" width="50%"><font>&#160; </font></td>
<td align="left" valign="top" width="40%">
<div align="left"><font>Name: Howard Benjamin</font></div>
</td>
<td valign="top" width="10%"><font>&#160; </font></td>
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<div><br>
&#160;</div>

<div>

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<hr align="left" noshade size="2" width="100%">
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</SEC-DOCUMENT>
