To evaluate the effectiveness of gammaglobulin in decreasing the incidence of coronary artery lesions in Kawasaki disease, a randomized controlled study in 136 patients was conducted using high doses of gammaglobulin 400 mg/kg/d for 3 days plus aspirin 30 mg/kg/d (gammaglobulin group) and aspirin alone at the same dosage (aspirin group). The total febrile period and the duration of fever after treatment were significantly shorter in the gammaglobulin group than in the aspirin group (P less than 0.001). The incidence of coronary artery lesions and of coronary artery aneurysms was significantly lower in the gammaglobulin group than in the aspirin group up to 30 days after the onset of Kawasaki disease (P less than 0.01 and P less than 0.05, respectively). In 16 of 69 patients given gammaglobulin, fever persisted for longer than 3 days, and there was a higher incidence of coronary artery lesions among them. The effectiveness of high doses of gammaglobulin in preventing coronary artery lesions has been demonstrated, but the indications and the optimal dose of gammaglobulin remain to be determined.