Polymerase chain reaction (PCR) was applied to detect HCV-RNA in 75 hemodialyzed patients. Anti-HCV status was determined by ELISA-2 and by RIBA-2 for reactive samples by ELISA. ALT levels were monthly determined during the year preceding the end of the study. For 60 patients, anti-HCV serology was known since 1989 and 39 of them were tested for the presence of HCV-RNA at least four times during the 2 preceding years. The 9 patients who were negative for anti-HCV antibodies were negative by PCR. Of the 7 patients with an indeterminate profile by RIBA-2, 3 were positive by PCR: 1/1 with C-33c band only and 2/6 with C22-3 band only. Of the 59 patients reactive by RlBA-2, 57 were HCV-RNA positive. Of the 2 HCV-RNA negative patients, one had been PCR positive before interferon therapy. Of the 38 patients without acute hepatitis tested by PCR on 5 successive samples, all the specimens of 11 and 23 patients were HCV-RNA negative and HCV-RNA positive respectively. In 4 patients, a transient viremia was observed. The group of HCV-RNA positive patients had mean ALT levels greater than those who were negative. A correlation was established between HCV infection and both the time on dialysis and the number of blood transfusions. A high concordance (97%) was observed between antibodies to HCV and HCV-RNA.