In order to delineate the efficacy of plasmin-treated intravenous gamma-globulin (IVGG) in the treatment of Kawasaki syndrome, we compared the frequency of coronary artery abnormalities in children treated or not with IVGG for Kawasaki syndrome. Among 291 cases of Kawasaki syndrome diagnosed during the period of 1987 to 1991 without coronary abnormalities within 10 days of the onset of illness, 128 were treated with IVGG and aspirin and were compared with 163 treated with aspirin alone. IVGG was given in a dosage of 400 mg/kg/day for 4 consecutive days. The detection of coronary abnormalities was monitored by two dimensional echocardiography. Two weeks after enrollment coronary artery abnormalities were present in 37 (22.7%) of 163 children in the aspirin group and in 9 (9%) of 128 in the gamma-globulin group (P < 0.05). Seven weeks after enrollment, abnormalities were present in 20 (12.3%) of 163 children in the aspirin group and in 6 (4.6%) of 128 in the IVGG group (P < 0.05). We conclude that plasmin-treated IVGG is effective in reducing the prevalence of coronary artery abnormalities in Kawasaki syndrome and suggest a predominant role of the Fc gamma fragment of IgG in the therapeutic effect.