Three interferon β preparations (Betaseron^®, Avonex^®, and Rebif^®) have shown efficacy in the treatment of relapsing-remitting multiple sclerosis (MS). Attack frequency is reduced by 30% and major attacks to an even greater extent. Accumulating disease burden as measured by annual T2-weighted magnetic resonance imaging is markedly lessened, and disease activity as measured by serial gadolinium-enhanced MRI scanning is reduced by over 80%. A fourth preparation, Copaxone^®, a basic copolymer of four amino acids, lessens MS attack frequency by 30% and also lessens disease activity as measured by gadolinium-enhanced MRI. Betaseron^® lessens accumulation of disability in MS patients with secondary progressive disease regardless of the severity of disability at the time treatment is commenced. MS is now a treatable disease.