PURPOSE: A prospective study was performed to evaluate the efficacies of two different dosages of aspirin(ASA) in treating Kawasaki disease(KD). METHODS: Thirty-nine children with KD were admitted to this hospital from July, 1992 to May, 1993, and were assigned randomly into 2 groups. Group A(medium-dose group, 20 patients) was given 50mg/kg/d(# 4), and group B(high-dose gorup, 19 patients) was given 100mg/kg/d(# 4) of ASA. Intravenous gammaglobulin(2g/kg) was given to all patients. RESULTS: 1) There were no significant differences in ages, sex ratios, durations of fever before treatment, and laboratory findings on admission between two groups. 2) The durations of ASA administration were similar in 2 groups(group A, 10.1+/-2.77 ; group B, 10.6+/-3.37 days ;?p>0.1). 3) The durations of fever after onset of treatment were not different significantly (group A, 2.65+/-3.28 ; group B, 1.74+/-1.52 days ; p>0.1). 4) There were no significant differences in laboratory findings after treatment between two groups, except hemoglobin(Hgb) and ESR examined in the 3 rd week of illness (Hgb: group A (N=15), 10.1+/-1.24 ; group B(n=14), 11.1+/-0.92g/dl ; p<0.05) (ESR: group A(n=14), 47.7+/-13.0 ; group B(n=14), 37.1+/-13.6mm/hr ; p<0.05). 5) Serum concentrations of ASA were examined 3 to 5 days after onset of treatment in 31 patients(group A, 17 ; group B, 14). Mean concentrations before the lst dose of the day were 3.28+/-3.01mg/dl in group A and 12.6+/-6.22mg/dl in group B(p<0.001). Mean concentrations before the 3 rd dose of the day were 3.58+/-2.36mg/dl in group A and 13.7+/-6.32mg/dl in group B(p<0.001). 6) EKG was examined 2 and 4 weeks after onset of illness. There were no abnormalities in EKG except sinus tachycardia in both groups. 7) Echocardiography was done 2 and 4 weeks after onset of illness. Coronary artery dilatation was observed in 40% of group A (8/20) and 31.6% of group B(6/19) at the lst examination (p>0.1), and in 25% of group A(5/20) and 10.5% of group B(2/19) at the 2 nd examination (p>0.1). In long-term follow-up, only 1 patient in each group showed coronary aneurysm respectively. CONCLUSIONS: Although serum concentrations of ASA were different significantly, there were no significant differences in recovery from KD and incidences of coronary artery lesions between two grous. So we think medium-dose aspirin therapy is safe and effective in the treatment of Kawasaki disease.