Objectives: To investigate serum concentrations of total bile acids (TBAs) in patients with acute Kawasaki syndrome (KS) and correlate those concentrations with other liver function test results. Patients and Methods: Seventy-one Japanese patients with KS (mean age, 1.6 years). Blood samples from 29 patients were obtained during the acute and convalescent phases of KS. Results: Elevated serum TEA concentrations higher than 20 mu mol/L were detected in 16 (22.5%) of the patients with acute KS. Serum concentrations of TBAs gradually returned to normal (P=.001, Pearson's correlation coefficient). The mean+/-SD serum concentration of TBAs of patients during the acute phase (37.9+/-63.9 mu mol/L) was significantly higher than that of patients during the convalescent phase (7.2+/-7.5 mu mol/L) (P=.02, Pearson's correlation coefficient). The data show a correlation between the serum concentrations of TBAs with those of alanine aminotransferase (P=.03, Pearson's correlation coefficient), total bilirubin (P<.001, Pearson's correlation coefficient), and C-reactive protein (P=.01, Pearson's correlation coefficient) measured during the acute phase. Conclusions: The cause of the elevated concentration of serum TBAs in patients with acute KS is unclear. Increased bile acid synthesis from cholesterol may occur, or patients with acute KS may suffer from damage to the bile duct cells of their biliary systems caused by cytokine activation. This damage may depress bile acid excretion, thereby increasing the serum concentrations of TBAs.