Exhibit 10.7

                                 SEVENTH AMENDMENT TO
                              REVOLVING CREDIT AGREEMENT
                                           

         THIS SEVENTH AMENDMENT TO REVOLVING CREDIT AGREEMENT (this "Seventh
Amendment") is made and entered into as of the 17th day of June, 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 BANKBOSTON, N.A. (formerly
known as 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, the Fifth Amendment
to Revolving Credit Agreement dated as of February 21, 1997, and the Sixth
Amendment to Revolving Credit Agreement dated as of March 17, 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 8.2(a) of the Credit Agreement. 

    Section 8.2(a) of the Credit Agreement is hereby deleted in its entirety
and the following substituted in place thereof: 

         "(a) the Borrowers will not create, incur or assume any Indebtedness
         other than (i) Indebtedness to the Bank; (ii) Indebtedness incurred
         after the date hereof in respect of the acquisition of property or in
         respect of new capital leases which does not exceed $500,000 in the
         aggregate; (iii) current liabilities of the Borrowers not incurred
         through the borrowing of money or the obtaining of credit except
         credit on an open account customarily extended; (iv) Indebtedness in
         respect of taxes or other governmental charges contested in good faith
         and by appropriate proceedings and for which adequate reserves have
         been taken; (v) 



         Indebtedness not included above and listed on Schedule 8.2(a) hereto 
         or on the Form 10-Q of the Parent dated March 31, 1995; (vi) 
         Indebtedness consisting of intercompany loans among the Borrowers 
         (except such loans as would render any of the Borrowers insolvent); 
         (vii) Indebtedness of BioDevelopment Laboratories, Inc. outstanding 
         at the time of acquisition thereof with respect to a standby letter 
         of credit issued by Silicon Valley Bank or any replacement thereof 
         in an aggregate amount not to exceed $157,500; (viii) Indebtedness 
         to the Guarantor arising under the Convertible Debt and Development 
         Funding Agreement dated as of March 29, 1996, as such agreement may 
         be amended, restated or supplemented from time to time, provided 
         that the principal amount of such Indebtedness shall not be 
         increased; and provided further that such Indebtedness is 
         subordinated to the Obligations on terms satisfactory to the Bank; 
         (ix) Indebtedness of (a) TSI Corporation to Finova Technology 
         Finance, Inc. (formerly Financing for Science International, Inc. 
         ("Finova")) pursuant to the terms of the Master Equipment Lease 
         Agreement dated as of September 27, 1994 by and between TSI 
         Corporation and Financing for Science International, Inc., and of 
         the Parent, Argus Research Laboratories, Inc., TSI Mason 
         Laboratories, Inc., TSI Redfield Laboratories, Inc., and TSI 
         Washington Laboratories, Inc. to Finova pursuant to guaranties of 
         such lease; and (b) the Parent to Transamerica Business Credit 
         Corporation ("TBCC") pursuant to the terms of the Master Lease 
         Agreement dated as of December 30, 1996 by and between TBCC and the 
         Parent, and of TSI Corporation, BioDevelopment Laboratories, Inc., 
         TSI Mason Laboratories, Inc., TSI Washington Laboratories, Inc., TSI 
         Redfield Laboratories, Inc., and Argus Research Laboratories, Inc. 
         to TBCC pursuant to guaranties of such lease, provided that the 
         aggregate outstanding amount of all such Indebtedness shall not 
         exceed $5,300,000; (x) Indebtedness of TSI Redfield Laboratories, 
         Inc. to Jefferson County, Arkansas in an aggregate principal amount 
         not to exceed $350,000, and Indebtedness of the Parent with respect 
         to the guaranty thereof; (xi) Indebtedness of TSI Redfield 
         Laboratories, Inc. to Simmons First National Bank in an aggregate 
         principal amount not to exceed $1,050,000, and Indebtedness of the 
         Parent and TSI Corporation with respect to the guaranty thereof; 
         (xii) Indebtedness of Argus Research Laboratories, Inc. to Unisys 
         Leasing Corporation in an aggregate principal amount not to exceed 
         $145,000 and Indebtedness of the Parent with respect to the guaranty 
         thereof; and (xiii) Indebtedness of TSI Mason Laboratories, Inc. to 
         the Massachusetts Development Finance Agency in an aggregate 
         principal amount not to exceed $5,000,000, and Indebtedness of the 
         Parent with respect to the guaranty thereof." 

    3.   Amendment to Section 8.2(b) of the Credit Agreement. 

    Section 8.2(b) of the Credit Agreement is hereby deleted in its entirety
and the following substituted in place thereof:

         "(b) the Borrowers will not create or incur any Liens on any of the 
         property or assets of the Borrowers except (i) Liens securing taxes 
         or other governmental charges not yet due; (ii) deposits or pledges 
         made in connection with social 



         security obligations; (iii) Liens of carriers, warehousemen, 
         mechanics and materialmen, less than 120 days old as to obligations 
         not yet due; (iv) easements, rights-of-way, zoning restrictions and 
         similar minor Liens which individually and in the aggregate do not 
         have a Materially Adverse Effect; (v) purchase money security 
         interests in or purchase money mortgages on real or personal 
         property securing purchase money Indebtedness permitted by Section 
         8.2(a)(ii), covering only the property so acquired; (vi) other Liens 
         existing on the date hereof and listed on Schedule 8.2(b) hereto or 
         existing on the date hereof and securing Indebtedness not to exceed 
         $500,000 in the aggregate; (vii) the rights of lessors under capital 
         leases permitted by Section 8.2(a) hereof; (viii) subject to the 
         terms and conditions of Section 8.2(a)(ii), purchase money liens on 
         the assets of any Subsidiary at the time such Subsidiary is acquired 
         by the Parent pursuant to Section 8.2(f) hereof, provided that such 
         Liens may cover only the property so acquired; (ix) mortgage Liens 
         on the real property owned by TSI Redfield Laboratories, Inc. in 
         favor of Jefferson County, Arkansas and Simmons First National Bank 
         securing Indebtedness permitted by Section 8.2(a)(x) and (xi) 
         hereof; (x) Liens on the personal property of TSI Redfield 
         Laboratories, Inc. securing the Indebtedness permitted by Section 
         8.2 (a)(xi) hereof; (xi) a mortgage Lien on the real property 
         located at 55 Union Street, Worcester, Massachusetts owned by TSI 
         Mason Laboratories, Inc. securing the Indebtedness permitted by 
         Section 8.2(a)(xiii) hereof; and (xii) Liens on the personal 
         property of TSI Mason Laboratories, Inc. purchased with the proceeds 
         of and securing the Indebtedness permitted by Section 8.2(a)(xiii) 
         hereof. 

    4.   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 Seventh 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 Seventh
Amendment. By executing this Seventh 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 Seventh Amendment. 

    5.   GOVERNING LAW.

    THIS SEVENTH--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.

    6.   Counterparts.  This Seventh 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.

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

    8.   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.

    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


                                       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


                                       BIODEVELOPMENT LABORATORIES, INC.


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




                                       THE BANK: 

                                       BANKBOSTON, N.A. (formerly known as The
                                       First National Bank of Boston) 


                                       By: /s/ Walter J. Marullo
                                       Name:Walter J. Marullo
                                       Title: Vice President

                                       Address: 

                                       100 Federal Street
                                       Boston, MA 02110
                                       Tel: 617-434-5462
                                       Fax: 617-434-0819

ACCEPTED AND AGREED TO BY: 

The Guarantor

GENZYME CORPORATION


By: /s/ Evan Lebson

Title: Vice President and Treasurer