The prevalence of antibody to hepatitis C virus (anti-HCV) was determined in 564 patients and 145 staff members of nine hemodialysis (HD) units in Nagano Prefecture using an enzyme-linked immunosorbent assay based on the C 100 HCV antigen (the first generation anti-HCV assay). And also serum HBV markers were tested in these subjects. One hundred patients (18%) were anti-C100 HCV positive, indicating that this figure represents a much higher prevalence than that (0.9%) among general population in the same geographical area. Out of 141 patients without history of blood transfusion, 17 (12%) were positive for anti-C 100 HCV, suggesting that blood-transfusions-unrelated acquisition of HCV infection can occur. Anti-HCV prevalence correlated with both the blood units transfused and the duration of HD treatment. There was a significant difference in the prevalence of anti-C 100 HCV in individual dialysis units ranging from 0% to 53%. In the dialysis unit with prevalence of 53%, approximately half of the anti-HCV positive patients were found to have chronic liver disease. The prevalence of hepatitis B virus (HBV) markers among HD patients, on the other hand, was 36% (202/564). Fifty one (51%) of 100 anti-C 100 HCV positive patients and 151 (33%) of 464 anti-C 100 HCV negative patients were positive for HBV markers, with significant difference in HBV infection rate between the 2 groups. The prevalence of chronic liver disease, defined as abnormal serum transaminase levels for more than 6 months was significantly higher in anti-HCV positive patients than in anti-HCV negative ones (39% vs 10%, p less than 0.05), suggesting that HCV infection may contribute to chronic liver disease in HD patients. Among 145 staff members, only 3 (2%) were positive for anti-HCV, whereas 25 (17%) were positive for hepatitis B core antibody (anti-HBc), indicating prior HBV infection. With applying the second generation anti-HCV assay, which can detect antibodies to both capsid and nonstructural products of HCV gene, anti-HCV prevalence increased by two times in HD patients, but didn't change in HD staff members.(ABSTRACT TRUNCATED AT 400 WORDS)