<SEC-DOCUMENT>0001274737-20-000063.txt : 20200702
<SEC-HEADER>0001274737-20-000063.hdr.sgml : 20200702
<ACCEPTANCE-DATETIME>20200702084253
ACCESSION NUMBER:		0001274737-20-000063
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20200618
FILED AS OF DATE:		20200702
DATE AS OF CHANGE:		20200702

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			PALLARES EBETUEL
		CENTRAL INDEX KEY:			0001614597

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-39049
		FILM NUMBER:		201007300

	MAIL ADDRESS:	
		STREET 1:		C/O EXAGEN INC.
		STREET 2:		1261 LIBERTY WAY, SUITE C
		CITY:			VISTA
		STATE:			CA
		ZIP:			92081

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			EXAGEN INC.
		CENTRAL INDEX KEY:			0001274737
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-MEDICAL LABORATORIES [8071]
		IRS NUMBER:				000000000
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1261 LIBERTY WAY
		CITY:			VISTA
		STATE:			CA
		ZIP:			92081
		BUSINESS PHONE:		(760) 560-1501

	MAIL ADDRESS:	
		STREET 1:		1261 LIBERTY WAY
		CITY:			VISTA
		STATE:			CA
		ZIP:			92081

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	EXAGEN DIAGNOSTICS INC
		DATE OF NAME CHANGE:	20031230
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_159369365100589.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-06-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001274737</issuerCik>
        <issuerName>EXAGEN INC.</issuerName>
        <issuerTradingSymbol>XGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001614597</rptOwnerCik>
            <rptOwnerName>PALLARES EBETUEL</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O EXAGEN INC.</rptOwnerStreet1>
            <rptOwnerStreet2>1261 LIBERTY WAY</rptOwnerStreet2>
            <rptOwnerCity>VISTA</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92081</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option(right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>13.0</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-06-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>9000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2030-06-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9000.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>9000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The entire number of shares subject to this option becomes fully vested and exercisable on the first to occur of (a) the first anniversary of the grant date or (b) the next occurring annual meeting of the Issuer's stockholders, subject to the Reporting Person's continued service on the board of directors of the Issuer through such vesting date.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Kamal Adawi, Attorney-in-Fact</signatureName>
        <signatureDate>2020-07-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
