We studied the effect of gamma-globulin (IVGG) and aspirin (ASA) on the development of the coronary artery lesions (CAL) of Kawasaki disease (KD) in three different protocols. Within 29 days of the onset of KD the echocardiographic evidence of CAL had developed in 39-42% of the patients in the ASA group, but only in 13.7-20.8% of the patients treated with IVGG (200 or 400 mg/kg X 5). In long-term follow-up observation of CAL of these patients the evidence of CAL in both the ASA and the IVGG group regressed gradually; however, the residual rate of CAL was significantly low in the IVGG group at all times up to 24 months after onset. These facts suggest that when using IVGG for KD, we should select a dose of intact gamma-globulin, 1,000 mg/kg or more in total, to prevent the occurrence of CAL. We have demonstrated not only a significant reduction in the occurrence of CAL in patients treated with IVGG but a reduction in the residual rate of CAL for two years as compared with those treated by ASA.