A high prevalence of anti-C100-3 antibodies has been reported in chronic hemodialysis patients. It is, however, unclear whether the results reflect true hepatitis C virus (HCV) infection in these patients, since false-positive results have been reported with this antibody assay. In the present study, plasma from 184 hemodialysis patients (110 males, 74 females) was examined for HCV-RNA by a reverse transcription-polymerase chain reaction method. Anti-C100-3 antibodies, second generation HCV antibodies, and anti-GOR antibodies were also examined by the respective EIAs. The positive rate of anti-C100-3 in the hemodialysis patients was 10.7% (20/184), which was significantly higher than the reported findings in the general population (P < 0.01). Using a second generation HCV antibody assay, the positive rate increased to 22%. HCV-RNA was detected in 15 of 184 patients (8.2%); 5 of 20 C100-3-positive patients (25%), and 10 of 164 C100-3-negative patients (6.1%). Serum alanine aminotransferase and gamma globulin levels were significantly higher in the patients with these HCV markers than those that were negative, while the history of blood transfusion was not related to the rate of the HCV markers. It is concluded that some hemodialysis patients have latent HCV infections that cannot be detected by currently available HCV antibody assays or routine biochemical liver function tests, and that the routes of transmission are not solely through blood transfusion.