A minimum of 31 evaluable HD patients were required for the ATryn® treatment trial. Results for 14 of these patients were already obtained from the previous study that supported ATryn®’s approval in the European Union for HD patients undergoing surgical procedures. Seventeen evaluable patients have been treated to complete the pivotal study. There were no clinically relevant DVTs or other thromboembolisms during the evaluation period in any of the patients treated in the pivotal study.

The previously completed comparator arm of the study is based on historical data gathered under a prospective clinical protocol from patients who had been previously treated with plasma-derived antithrombin products while undergoing similar high-risk procedures to those performed in the active arm. There were no clinically relevant DVTs or other thromboembolisms in these patients.

“Completing enrollment in this pivotal study is another important stepping stone in validating the application of our transgenic production technology to the development of recombinant protein therapeutics. We look forward to completing our rolling Biologics License Application as planned around mid-2008, when we submit the full clinical data package,” stated Geoffrey F. Cox, PhD, GTC’s Chairman and CEO. “ATryn® is unique in being the only recombinant form of human antithrombin to be developed for therapeutic use, as recognized in its orphan drug status for the HD indication.”

The full clinical data package will include 90-day follow-up tests for antibody generation to ATryn®, which is a typical regulatory requirement and was also part of the approval process successfully completed for the European Union.

About GTC Biotherapeutics

GTC Biotherapeutics develops, supplies, and commercializes therapeutic proteins produced through transgenic animal technology. In addition to ATryn®, GTC is developing a portfolio of recombinant human plasma proteins with known therapeutic properties. These proteins include recombinant forms of human coagulation factors VIIa, VIII, and IX, which are used for the treatment of hemophilia, and alpha-1 antitrypsin. GTC also has a monoclonal antibody portfolio that includes a monoclonal antibody to CD20 and a monoclonal antibody to CD137. GTC’s intellectual property includes a patent in the United States through 2021 for the production of any therapeutic protein in the milk of any transgenic mammal. GTC’s transgenic production platform is particularly well suited to enabling cost effective development of proteins that are difficult to express in traditional recombinant production systems as well as proteins that are required in large volumes. Additional information is available on the GTC web site, http://www.gtc-bio.com.

This press release contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995, including without limitation statements regarding the timing of availability of antibody generation results, and filing of the associated rolling Biologics License Application. Such forward-looking statements are subject to a number of risks, uncertainties and other factors that could cause actual results to differ materially from future results expressed or implied by such statements. Factors that may cause such differences include, but are not limited to, the risks and uncertainties discussed in GTC's most recent Annual Report on Form 10-K and its other periodic reports filed with the Securities and Exchange Commission, including the uncertainties associated with conducting clinical studies, and the risks and uncertainties associated with dependence upon the actions of regulatory agencies. GTC cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this document, and GTC undertakes no obligation to update or revise the statements, except as may be required by law