<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
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        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001820958</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <issuerInfo>
            <issuerCik>0000310158</issuerCik>
            <issuerName>MERCK &amp; CO. INC.</issuerName>
            <secFileNumber>001-06571</secFileNumber>
            <issuerAddress>
                <ns2:street1>2000 Galloping Hill Road</ns2:street1>
                <ns2:city>Kenilworth</ns2:city>
                <ns2:stateOrCountry>NJ</ns2:stateOrCountry>
                <ns2:zipCode>07033</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>908-740-4000</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>DAVID WILLIAMS</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>38th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>7509</noOfUnitsSold>
            <aggregateMarketValue>877222.41</aggregateMarketValue>
            <noOfUnitsOutstanding>2538592467</noOfUnitsOutstanding>
            <approxSaleDate>05/02/2023</approxSaleDate>
            <securitiesExchangeName>NYSE</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>05/03/2020</acquiredDate>
            <natureOfAcquisitionTransaction> Restricted Stock Units Vested Under Issuer S-8 Reg Plan</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>3021</amountOfSecuritiesAcquired>
            <paymentDate>05/03/2020</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>05/04/2018</acquiredDate>
            <natureOfAcquisitionTransaction>Exercise of Employee Stock Options under Issuer S-8 Reg Plan</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>4487</amountOfSecuritiesAcquired>
            <paymentDate>05/04/2018</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>02/20/2021</acquiredDate>
            <natureOfAcquisitionTransaction> Restricted Stock Units Vested Under Issuer S-8 Reg Plan</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>1</amountOfSecuritiesAcquired>
            <paymentDate>02/20/2021</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>05/02/2023</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ DAVID MICHAEL WILLIAMS</signature>
        </noticeSignature>
    </formData>
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144
0001820958
XXXXXXXX
LIVE
0000310158
MERCK & CO. INC.
001-06571
2000 Galloping Hill Road
Kenilworth
NJ
07033
908-740-4000
DAVID WILLIAMS
Officer
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Floor
New York
NY
10004
7509
877222.41
2538592467
05/02/2023
NYSE
Common
05/03/2020
Restricted Stock Units Vested Under Issuer S-8 Reg Plan
Issuer
N
3021
05/03/2020
Not Applicable
Common
05/04/2018
Exercise of Employee Stock Options under Issuer S-8 Reg Plan
Issuer
N
4487
05/04/2018
Cash
Common
02/20/2021
Restricted Stock Units Vested Under Issuer S-8 Reg Plan
Issuer
N
1
02/20/2021
Not Applicable
Y
05/02/2023
/s/ DAVID MICHAEL WILLIAMS