Among the 35.210 patients with Kawasaki disease who were reported in nationwide surveys from 1991 to 1996, 83% were treated with gamma-globulin (GG). Those treated with a total dose of 1000 mg/kg (9098 patients) and 2000 mg/kg (7012 patients) were selected as the subjects of the study on the relationship between the development of cardiac sequelae, in particular of giant aneurysms, and related factors using logistic regression models. Among the two groups that received 1000 mg/kg and 2000 mg/kg, respectively, the odds ratios for cardiac sequelae were significantly high for males, those < 6 months and > or = 7 years of age, and typical or recurrent cases. Except for those < 6 months of age, the odds ratios of all the factors mentioned above were higher for the incidence of giant coronary aneurysms than those for cardiac sequelae. The preventive effects of GG therapy for cardiac sequelae and in particular giant aneurysms, were significantly low when GG administration was initiated on day 8 or later after onset. In the group treated with 1000 mg/kg, the preventive effect was low when GG administration was spread over 3 days or longer. To prevent the development of cardiac sequelae, in particular giant coronary aneurysms, gamma-globulin therapy should be started as soon as possible and be completed within 2 days.