SUMMARY.Patients on maintenance haemodialysis in four dialysis centres were tested for markers of hepatitis C virus (HCV) infection. Antibody to HCV (anti‐HCV) was detected by the second‐generation enzyme immunoassay in 142 (26%) of the 543 patients and HCV RNA in 117 (22%) of whom four were without detectable anti‐HCV in serum. Seventy‐seven (66%) were infected with HCV of genotype II/1b, 31 (27%) with genotype III/2a and eight (7%) with genotype IV/2b. in a distribution similar to that in blood donors who carried HCV asymptomatically. Haemodialysis patients had high HCV RNA titres comparable to those of patients with chronic hepatitis C. HCV RNA was detected in 96 (26%) of the 365 patients with a history of transfusion more frequently than in 21 (12%) of the 178 without previous transfusion (P<0.001). In transfused patients, frequencies of anti‐HCV and HCV RNA increased in parallel with the duration of haemodialysis. The frequency of anti‐HCV in non‐transfused patients, however, did not change appreciably with the duration of haemodialysis up to 22 years. The patients with anti‐HCV had a higher frequency of HCV RNA in serum than symptom‐free blood donors with anti‐HCV (113/142 or 80%vs109/166 or 66%P<0.01) and the patients with HCV RNA had a lower frequency of elevated aminotransferase levels than blood donors with HCV RNA (5/113 or 4%vs27/109 or 25%,P<0.00l). These results indicate that transfusion is a significant cause of HCV infection in patients on maintenance haemodialysis, and that these patients are prone to establish the HCV carrier st