The aim of this study was the detection of HCV viremia in both anti-HCV antibody positive and negative hemodialysis patients. Sera from 75 patients on extracorporeal blood purification in the same dialysis unit were analyzed. Anti-HCV antibodies were detected using a 2nd-generation ELISA assay and in all positive cases a RIBA 3rd-generation test was performed. HCV-RNA was tested by a reverse transcription-nested polymerase chain reaction (RT-PCR) assay with primers located in the 5' region. PCR products were analyzed by a nonradioactive hybridation assay. The presence of anti-HCV antibodies was detected in 30 (40%) patients by means of ELISA II test; 28 of them were RIBA III positive and two indeterminate. Twenty-four of the 30 HCV Ab ELISA II positive patients (80%) were HCV-RNA positive (23 RIBA III positive and 1 indeterminate). Six anti-HCV Ab ELISA II positive patients tested negative for HCV-RNA (20%); 5 of these patients were also positive for anti-HCV antibodies with a RIBA III test and 1 was indeterminate. None of the anti-HCV negative patients was HCR-RNA positive. In two cases we documented the disappearance of viremia after an acute HCV infection, with the persistence of antibody reactivity. In conclusion, anti-HCV antibody positive hemodialysis patients should be considered as potentially infectious.