Copolymer I (Copaxone) was evaluated in a multicenter, placebo-controlled, double-blind trial at 11 US universities. Two hundred and fifty-one relapsing-remitting ambulatory MS patients were randomized to receive 20 mg of copolymer 1 or placebo by daily subcutaneous injection for approximately 30 months. At conclusion, the copolymer 1 group had 32% fewer relapses (P=0.002) and significantly more were relapse-free (P=0.035). Significantly, more patients were receiving copolymer 1 had improved during the study, while more patients on placebo showed neurological decline (P=0.001). There were few side effects and no drug related laboratory abnormalities. Copolymer 1 is being considered by North American and European regulatory agencies for approval as a commercially available agent for the control of multiple sclerosis.