To evaluate the meaning of anti-HCV detection in patients treated with IVIG, serum levels of aspartate aminotranstferase(AST), alanine aminotransterase(ALT), HCV Ab titer were measured after treatment with IVIG in 36 patients diagnised of Kawasaki disease or neonatal sepsis. Also polymerase chain reaction (PCR) for the detection of HCV was done in 8 patients with persistent HCV Ab positivity at 3 months after IVIG treatment. The results were as follows 1) HCV Ab was positive in all 36 patients at 1 week after IVIG treatment, but in only 8 cases it was positive at 3 months after IVIG treatment. 2) AST, ALT were elevated in 9 cases at 1 week after IVIG treatment, but they were normalized in all cases at 3 months after IVIG treatment. 3) PCR for the detection of HCV was done in 8 patients with persistent HCV Ab positivity at 3 months after IVIG treatment, but HCV was not isolated in any cases. These results suggested that detection of anti-HCV was merely transitory phenominon of HCV Ab transmission, did not show any evidence of HCV infection due to HCV transmission.