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                                                                 EXHIBIT 10.27.7

                                                                                

                                  SIXTH AMENDMENT TO
                              REVOLVING CREDIT AGREEMENT


            THIS SIXTH AMENDMENT TO REVOLVING CREDIT AGREEMENT (this "Sixth 
Amendment") is made and entered into as of the seventeenth day of March, 
1997, by and among GENZYME TRANSGENICS CORPORATION, a Massachusetts 
corporation having its principal place of business at One Mountain Road, 
Framingham, Massachusetts 01701 (the "Parent") and its Subsidiaries listed on 
the signature pages hereto (the Parent and each such Subsidiary is 
individually referred to herein as a "Borrower," and collectively as the 
"Borrowers"), and THE FIRST NATIONAL BANK OF BOSTON (the "Bank"), a national 
banking association with its head office at 100 Federal Street, Boston, 
Massachusetts 02110.

            WHEREAS, the Borrowers and the Bank entered into a Revolving 
Credit Agreement dated as of July 3, 1995 as amended by the First Amendment 
to Revolving Credit Agreement dated as of September 15, 1995, the Second 
Amendment to Revolving Credit Agreement dated as of December 22, 1995, the 
Third Amendment to Revolving Credit Agreement dated as of March 29, 1996, the 
Fourth Amendment to Revolving Credit Agreement dated as of October 1, 1996 
and the Fifth Amendment to Revolving Credit Agreement dated as of February 
21, 1997 (as further amended and in effect from time to time, the "Credit 
Agreement") pursuant to which the Bank extended credit to the Borrowers on 
the terms set forth therein;

            WHEREAS, the Bank and the Borrowers have agreed to amend the 
Credit Agreement as hereinafter set forth;

            NOW, THEREFORE, for good and valuable consideration the receipt 
and sufficiency of which is hereby acknowledged, the parties hereto agree as 
follows:

            1.   Definitions.  Capitalized terms used herein without 
definition have the meanings ascribed to them in the Credit Agreement.

            2.   Amendment to Section 1.1.  The definition of "Maturity Date" 
appearing in Section 1.1 of the Credit Agreement is hereby deleted in its 
entirety and the following substituted in place thereof:

                 "Maturity Date.  March 31, 1999, or any later date to which  
           such date may be extended pursuant to Section 2.5 hereof."

            3.   Amendment to Section 2.2.  The first sentence of Section 2.2 
of the Credit Agreement is hereby amended by deleting the phrase "the 
Eurodollar Rate plus three quarters of one percent (3/4%)," appearing therein 
and substituting the phrase "the Eurodollar Rate plus one half of one percent 
(1/2%)," in place thereof.

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            4.   Amendment to Section 2.5.  Section 2.5 of the Credit 
Agreement is hereby deleted in its entirety and the following substituted in 
place thereof:

                 "Extension of Maturity Date.  At least sixty (60) days but not
            more than ninety (90) days prior to (i) March 31, 1998 and
            (ii) March 31 of any year thereafter, the Borrowers may request in
            writing that the Maturity Date be extended for an additional one
            year period beyond the then-applicable Maturity Date.  Not later
            than thirty (30) days after the date of the Borrowers' request, the
            Bank will notify the Borrowers whether, in its sole discretion, it
            is willing to consent to such one-year extension.  If the Bank
            shall agree to extend the Maturity Date, then this Agreement shall
            be deemed to be amended to reflect such extension and all the terms
            and conditions hereof shall continue in full force and effect
            during such extended period." 

            5.   Ratification, etc. 

            Except as expressly amended hereby, the Credit Agreement, the 
other Loan Documents and all documents, instruments and agreements related 
thereto are hereby ratified and confirmed in all respects and shall continue 
in full force and effect.  This Sixth Amendment and the Credit Agreement 
shall hereafter be read and construed together as a single document, and all 
references in the Credit Agreement or any related agreement or instrument to 
the Credit Agreement shall hereafter refer to the Credit Agreement as amended 
by this Sixth Amendment.  By executing this Sixth Amendment where indicated 
below, the Guarantor hereby ratifies and confirms its guaranty of the 
Obligations pursuant to the terms of the Guaranty, as amended, and 
acknowledges and consents to the terms of this Sixth Amendment.

            6.   GOVERNING LAW.

            THIS SIXTH AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED IN 
ACCORDANCE WITH THE LAWS OF THE COMMONWEALTH OF MASSACHUSETTS AND SHALL TAKE 
EFFECT AS A SEALED INSTRUMENT IN ACCORDANCE WITH SUCH LAWS.

            7.   Counterparts.  This Sixth Amendment may be executed in any 
number of counterparts and by different parties hereto on separate 
counterparts, each of which when so executed and delivered shall be an 
original, but all of which counterparts taken together shall be deemed to 
constitute one and the same instrument.  A complete set of counterparts shall 
be lodged with the Bank.

            8.   Effectiveness.  This Sixth Amendment shall become effective 
upon its execution and delivery by the respective parties hereto.

            9.   Entire Agreement.  THE CREDIT AGREEMENT AS AMENDED 
REPRESENTS THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE 
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS, OR SUBSEQUENT ORAL 
AGREEMENTS OF THE PARTIES.  THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN 
THE PARTIES. 

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            IN WITNESS WHEREOF, the undersigned have duly executed this 
Agreement under seal as of the date first set forth above.

                                     THE BORROWERS:

                                     GENZYME TRANSGENICS CORPORATION



                                     By: /s/ John B. Green
                                         ---------------------------
                                          Name:  John B. Green
                                          Title:  Vice President


                                     Address of the Parent:

                                     One Mountain Road
                                     Framingham, MA  01701
                                     Tel:  (508) 872-8400
                                     Fax:  (508) 872-0827


                                     TSI CORPORATION



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                     TSI MASON LABORATORIES INC.



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President



                                     TSI WASHINGTON LABORATORIES, INC.



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                      3

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                                     TSI REDFIELD LABORATORIES, INC.



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                     ARGUS RESEARCH LABORATORIES, INC.



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                     TRANSGENIC INVESTMENTS, INC.



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                     HEALTH AND SCIENCES RESEARCH
                                      INCORPORATED



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                     THE TSI CENTER FOR DIAGNOSTIC
                                      PRODUCTS, INC.
                                                                   



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                         4
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                                     BIODEVELOPMENT LABORATORIES, INC.



                                     By: /s/ John B. Green
                                         ----------------------------
                                          Title:  Vice President


                                     THE BANK:

                                     THE FIRST NATIONAL BANK OF BOSTON



                                     By: /s/ Elizabeth C. Everett
                                         ----------------------------
                                          Name:  Elizabeth C. Everett
                                          Title:  Vice President

                                     Address:

                                     100 Federal Street
                                     Boston, MA 02110
                                     Tel:   617-434-2318
                                     Fax:  617-434-0819  



ACCEPTED AND AGREED
TO BY:

The Guarantor:

GENZYME CORPORATION


By: /s/ Evan M. Lebson
    --------------------------------
Title:  Vice President and Treasurer


                                         5