Exhibit 32

CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO

SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report on Form 10-Q of the GTC Biotherapeutics, Inc. (the “Company”) for the quarterly period ended April 1, 2007, as filed with the Securities and Exchange Commission on the date hereof, (the “Report”), each of the undersigned hereby certifies, pursuant to 18 U.S.C. Section 1350, that:

(1) The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(2) The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Date: May 3, 2007	/s/ Geoffrey F. Cox
	Geoffrey F. Cox
	Chairman of the Board, President and Chief Executive Officer
Date: May 3, 2007	/s/ John B. Green
	John B. Green
	Senior Vice President, Chief Financial Officer and Treasurer