Results of serologic tests were correlated with hepatitis C virus (HCV) viremia, determined by a cDNA polymerase chain reaction assay to detect HCV RNA, in 340 Danish dialysis patients; of these, 28 (8.2%) were positive for antibodies to HCV (anti-HCV) with second-generation ELI-SAs. HCV RNA was found in sera from 27 of these 28 anti-HCV-positive patients. However, 8 dialysis patients had detectable levels of HCV RNA but were anti-HCV-negative with second-generation ELISAs. Among the 35 HCV-infected dialysis patients 16 were positive, 7 indeterminate, and 12 negative with the second-generation RIBA. More than 60% of patients with evidence of ongoing liver disease had HCV infection. Thus, current commercially available antibody tests did not accurately reflect the HCV status in dialysis patients. A relatively high prevalence (> 10%) of HCV RNA, closely associated with liver disease, was found among dialysis patients in a low-prevalence area of the world.