We have done cross sectional and prospective studies to determine the prevalence and the clinical significance of antibodies to the hepatitis C virus (Anti-HCV) in 54 hemodialysis (HD) patients and 227 continuous ambulatory peritoneal dialysis (CAPD) patients. Fifteen patients (27.8%) were anti-HCV (+) among the HD group, and twelve patients (5.3%) were anti-HCV (+) among the CAPD group. In the HD group, the positivity of anti-HCV correlated with the duration of HD, but there was no significant correlation with the history of transfusion, the amount of transfusion and abnormal alanine aminotransferase (ALT). At the follow-up study in 164 cases (HD 50 cases, CAPD 114 cases) after 6 months, one of 14 anti-HCV (+) CAPD patients was converted to anti-HCV (-) and two of 35 anti-HCV (-) HD patients were converted to anti-HCV (+). In conclusion, the prevalence of anti-HCV was significantly higher in HD patients compared to CAPD patients, and the positivity for anti-HCV in HD patients correlated with the duration of HD. A regular follow-up of anti-HCV and isolation of anti-HCV (+) HD patients with a separate machine may be needed to prevent the transmission of the hepatitis C virus during hemodialysis.