Among patients undergoing maintenance hemodialysis, a high prevalence of hepatitis C virus (HCV) infection can be observed. In a prospective study, sera of 273 patients were examined for the presence of HCV infection by serological tests and by PCR. Thirty-five patients (12.8%) were HCV antibody positive, and in 31 of them HCV RNA could be detected by PCR. Among the 238 seronegative patients HCV infection was detected in 12 cases (5.0%) exclusively by PCR. Only in 1 of these patients seroconversion could be observed within the 18-month follow-up period. These findings demonstrate that in hemodialysis patients PCR is necessary for the diagnosis of HCV infection.