Serum salicylate concentrations were measured in 60 patients with acute phase Kawasaki disease (KD), who were treated with intravenous aspirin (IVASP), to evaluate its anti-inflammatory effect in the treatment of KD. Patients with serum salicylate concentrations > or = 150 micrograms/ml showed shorter durations of fever (7.1 +/- 2.0 vs 10.4 +/- 6.6 days; P < 0.05), shorter durations of positive serum C-reactive protein (14.6 +/- 4.5 vs 22.3 +/- 10.6 days; P < 0.01) and lower incidences of coronary arterial involvements (0/10 vs 6/24; P < 0.05) than did patients with serum salicylate concentrations < 150 micrograms/ml. Significant linear correlations were recognized between daily IVASP dosage and serum salicylate concentrations (r = 0.73; P < 0.01), and between serum salicylate concentrations and serum free salicylate concentrations (r = 0.82; P < 0.01). These correlations did not differ between the presence and absence of coronary arterial involvements. Based on these findings we concluded that a beneficial anti-inflammatory effect in the treatment of KD is achieved when the serum salicylate concentration is > or = 150 micrograms/ml, and that such concentrations could be achieved by increasing the daily IVASP dosage to 100 mg/kg per day or more.