Sydenham's chorea has been established as a postinfectious autoimmune neuropsychiatric disorder. Corticosteroids have been used to treat patients with severe disease but are not always effective, and relapses are frequent after cessation. Eighteen subjects were entered into this randomized-entry controlled trial designed to determine if intravenous immunoglobulin or plasma exchange would be superior to prednisone in decreasing the severity of chorea. Mean chorea severity for the entire group was significantly lower at the 1-month follow-up evaluation (overall 48% improvement). Although the between-group differences were not statistically significant, clinical improvements appeared to be more rapid and robust in the intravenous immunoglobulin and plasma exchange groups than in the prednisone group (mean chorea severity scores decreased by 72% in the intravenous immunoglobulin group, 50% in the plasma exchange group, and 29% in the prednisone group). Larger studies are required to confirm these clinical observations and to determine if these treatments are cost-effective for this disorder.