European Commission Approves ATryn(R).

FRAMINGHAM, Mass. -- GTC Biotherapeutics, Inc. ("GTC", Nasdaq: GTCB) reported today that the European Commission has granted market authorization to ATryn(R), GTC's recombinant form of human antithrombin, for the prophylaxis of venous thromboembolism in surgery of patients with congenital antithrombin deficiency. Antithrombin is a naturally occurring plasma protein that has both anticoagulant and anti-inflammatory properties. GTC produces ATryn(R) in the milk of goats that have a transgene for human antithrombin. ATryn(R) is the first transgenically produced protein to be approved for human therapeutic use anywhere in the world. ATryn(R) is also the first recombinant antithrombin product approved anywhere in the world and the first antithrombin product, whether recombinant or derived from the human blood supply, that has been approved through the centralized EMEA procedure for use in all 25 countries of the European Union.

"The approval of ATryn(R) by the European Commission is the final confirmation of a major achievement for GTC for which we are very proud," stated Geoffrey F. Cox, Ph.D., GTC's Chairman of the Board and Chief Executive Officer. "This approval represents validation of our technology and the beginning of a new phase of opportunities for GTC to build a significant company."

The European Commission approval follows on the positive opinion determined by the Committee for Medicinal Products for Human Use of the European Medicines Agency on June 2, 2006. The positive opinion was based on an extensive review of the application submitted in January 2004.

Patients with a hereditary antithrombin deficiency are prone to developing blood clots. These patients may normally be maintained on an oral blood thinning agent. When a hereditary deficient patient is undergoing a high risk procedure, such as surgery, the blood thinning medication is typically discontinued to minimize the risk of excessive bleeding. Supplementation of low antithrombin levels with ATryn(R) may be utilized during these high risk procedures to allow for appropriate functioning of the natural coagulation management system. ATryn(R) is administered by infusion in a hospital setting during the high risk procedure. The hereditary deficient population is estimated to be about 1 in 5,000 and has been dependent upon plasma-derived antithrombin products for use during high risk procedures. GTC's recombinant form of antithrombin will offer an alternative to treatment with plasma-derived product and a consistent availability of product throughout the European Union, once reimbursement rates are obtained.

Negotiation of the reimbursement rates with each country's health system and establishment of sales and marketing efforts in Europe will be performed by GTC's partner, LEO Pharma A/S. GTC will continue to produce the product, receiving a transfer price from LEO as well as a royalty on commercial sales. Market launch is targeted for the second quarter of 2007 as reimbursement rates are finalized. LEO will also make a non-refundable $2 million milestone payment to GTC for receipt of the European market authorization.

About GTC Biotherapeutics, Inc.

GTC Biotherapeutics is a leader in the development, production, and commercialization of therapeutic proteins through transgenic animal technology. In addition to the ATryn(R) program, GTC has programs for a recombinant human alpha-1 antitrypsin, a recombinant human albumin, a CD137 antibody to stimulate the immune system as a potential treatment for solid tumors, and a malaria vaccine. In its external programs, GTC's technology is used to develop transgenic production of its partners' proprietary products, including both large-volume protein therapeutics as well as products that are difficult to produce in significant quantities from conventional recombinant production systems. One of the external programs is in clinical trials with a transgenically produced product. 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 the market launch of ATryn(R) and the negotiation of reimbursement rates. 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 as filed with the Securities and Exchange Commission, including the uncertainties associated with negotiating sufficient reimbursement rates, and the risks and uncertainties associated with dependence upon the actions of partners and national healthcare systems. 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.