<SEC-DOCUMENT>0001140361-12-045067.txt : 20121031
<SEC-HEADER>0001140361-12-045067.hdr.sgml : 20121031
<ACCEPTANCE-DATETIME>20121031155002
ACCESSION NUMBER:		0001140361-12-045067
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20121029
FILED AS OF DATE:		20121031
DATE AS OF CHANGE:		20121031

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			Synthetic Biologics, Inc.
		CENTRAL INDEX KEY:			0000894158
		STANDARD INDUSTRIAL CLASSIFICATION:	PHARMACEUTICAL PREPARATIONS [2834]
		IRS NUMBER:				133808303
		STATE OF INCORPORATION:			NV
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		3985 RESEARCH PARK DRIVE,
		STREET 2:		SUITE 200
		CITY:			ANN ARBOR
		STATE:			MI
		ZIP:			48108
		BUSINESS PHONE:		(734) 332-7800

	MAIL ADDRESS:	
		STREET 1:		3985 RESEARCH PARK DRIVE,
		STREET 2:		SUITE 200
		CITY:			ANN ARBOR
		STATE:			MI
		ZIP:			48108

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ADEONA PHARMACEUTICALS, INC.
		DATE OF NAME CHANGE:	20081027

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	PIPEX PHARMACEUTICALS, INC.
		DATE OF NAME CHANGE:	20061214

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	SHEFFIELD PHARMACEUTICALS INC
		DATE OF NAME CHANGE:	19970730

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KIRK RANDAL J
		CENTRAL INDEX KEY:			0001091823

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-12584
		FILM NUMBER:		121170789

	MAIL ADDRESS:	
		STREET 1:		1881 GROVE AVENUE
		CITY:			RADFORD
		STATE:			VA
		ZIP:			24141

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			INTREXON CORP
		CENTRAL INDEX KEY:			0001356090
		STATE OF INCORPORATION:			VA
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-12584
		FILM NUMBER:		121170790

	BUSINESS ADDRESS:	
		STREET 1:		1750 KRAFT DRIVE
		STREET 2:		SUITE 1400
		CITY:			BLACKSBURG
		STATE:			VA
		ZIP:			24060
		BUSINESS PHONE:		301-556-9809

	MAIL ADDRESS:	
		STREET 1:		1750 KRAFT DRIVE
		STREET 2:		SUITE 1400
		CITY:			BLACKSBURG
		STATE:			VA
		ZIP:			24060
</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>2012-10-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000894158</issuerCik>
        <issuerName>Synthetic Biologics, Inc.</issuerName>
        <issuerTradingSymbol>SYN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001091823</rptOwnerCik>
            <rptOwnerName>KIRK RANDAL J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O THIRD SECURITY, LLC</rptOwnerStreet1>
            <rptOwnerStreet2>1881 GROVE AVENUE</rptOwnerStreet2>
            <rptOwnerCity>RADFORD</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>24141</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001356090</rptOwnerCik>
            <rptOwnerName>INTREXON CORP</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O LEGAL DEPARTMENT</rptOwnerStreet1>
            <rptOwnerStreet2>20358 SENECA MEADOWS PARKWAY</rptOwnerStreet2>
            <rptOwnerCity>GERMANTOWN</rptOwnerCity>
            <rptOwnerState>MD</rptOwnerState>
            <rptOwnerZipCode>20876</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-10-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3125000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>1.60</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3125000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by NRM VII Holdings</value>
                    <footnoteId id="F1"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6675768</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>by Intrexon</value>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Randal J. Kirk controls NRM VII Holdings I, LLC (&quot;NRM VII Holdings&quot;).  Shares held by this entity may be deemed to be indirectly beneficially owned (as defined under Rule 13d-3 promulgated under the Securities Exchange Act of 1934, as amended) by Mr. Kirk.  Mr. Kirk disclaims beneficial ownership of such shares, except to the extent of any pecuniary interest therein.</footnote>
        <footnote id="F2">Randal J. Kirk, directly and through certain affiliates, has voting and dispositive power over a majority of the outstanding capital stock of Intrexon Corporation (&quot;Intrexon&quot;).  Mr. Kirk may therefore be deemed to have voting and dispositive power over the shares of the issuer owned by Intrexon.  Shares held by Intrexon may be deemed to be indirectly beneficially owned (as defined under Rule 13d-3 promulgated under the Securities Exchange Act of 1934, as amended) by Mr. Kirk.  Mr. Kirk disclaims beneficial ownership of such shares, except to the extent of any pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/  Randal J. Kirk</signatureName>
        <signatureDate>2012-10-31</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/  Randal J. Kirk, CEO Intrexon Corporation</signatureName>
        <signatureDate>2012-10-31</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
