<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
    <headerData>
        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001189403</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>STEVEN C. MIZELL</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>13400</noOfUnitsSold>
            <aggregateMarketValue>1594734.00</aggregateMarketValue>
            <noOfUnitsOutstanding>2538592467</noOfUnitsOutstanding>
            <approxSaleDate>05/03/2023</approxSaleDate>
            <securitiesExchangeName>NYSE</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>10/30/2021</acquiredDate>
            <natureOfAcquisitionTransaction>Restricted Stock Vested under Issuer S-8 Registered Plan</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>1400</amountOfSecuritiesAcquired>
            <paymentDate>10/30/2021</paymentDate>
            <natureOfPayment>Not Applicable</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>05/01/2020</acquiredDate>
            <natureOfAcquisitionTransaction>Exercise of Options under an Issuer S-8 Registered Plan</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>12000</amountOfSecuritiesAcquired>
            <paymentDate>05/01/2020</paymentDate>
            <natureOfPayment>Cash</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>Steven Mizell</name>
                <address>
                    <ns2:street1>2000 Galloping Hill Road</ns2:street1>
                    <ns2:city>Kenilworth</ns2:city>
                    <ns2:stateOrCountry>NJ</ns2:stateOrCountry>
                    <ns2:zipCode>07033</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>02/13/2023</saleDate>
            <amountOfSecuritiesSold>1815</amountOfSecuritiesSold>
            <grossProceeds>197951.00</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>Steven Mizell</name>
                <address>
                    <ns2:street1>2000 Galloping Hill Road</ns2:street1>
                    <ns2:city>Kenilworth</ns2:city>
                    <ns2:stateOrCountry>NJ</ns2:stateOrCountry>
                    <ns2:zipCode>07033</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>02/09/2023</saleDate>
            <amountOfSecuritiesSold>5000</amountOfSecuritiesSold>
            <grossProceeds>534837.00</grossProceeds>
        </securitiesSoldInPast3Months>
        <securitiesSoldInPast3Months>
            <sellerDetails>
                <name>Steven Mizell</name>
                <address>
                    <ns2:street1>2000 Galloping Hill Road</ns2:street1>
                    <ns2:city>Kenilworth</ns2:city>
                    <ns2:stateOrCountry>NJ</ns2:stateOrCountry>
                    <ns2:zipCode>07033</ns2:zipCode>
                </address>
            </sellerDetails>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <saleDate>02/06/2023</saleDate>
            <amountOfSecuritiesSold>4436</amountOfSecuritiesSold>
            <grossProceeds>462323.00</grossProceeds>
        </securitiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>05/03/2023</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ Steven Craig Mizell</signature>
        </noticeSignature>
    </formData>
</edgarSubmission>
[{"type": "144", "sequence": "1", "filename": "primary_doc.xml", "secsgml_size_bytes": 5977}]
144
0001189403
XXXXXXXX
LIVE
0000310158
MERCK & CO. INC.
001-06571
2000 Galloping Hill Road
Kenilworth
NJ
07033
908-740-4000
STEVEN C. MIZELL
Officer
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
38th Floor
New York
NY
10004
13400
1594734.00
2538592467
05/03/2023
NYSE
Common
10/30/2021
Restricted Stock Vested under Issuer S-8 Registered Plan
Issuer
N
1400
10/30/2021
Not Applicable
Common
05/01/2020
Exercise of Options under an Issuer S-8 Registered Plan
Issuer
N
12000
05/01/2020
Cash
N
Steven Mizell
2000 Galloping Hill Road
Kenilworth
NJ
07033
Common
02/13/2023
1815
197951.00
Steven Mizell
2000 Galloping Hill Road
Kenilworth
NJ
07033
Common
02/09/2023
5000
534837.00
Steven Mizell
2000 Galloping Hill Road
Kenilworth
NJ
07033
Common
02/06/2023
4436
462323.00
05/03/2023
/s/ Steven Craig Mizell