Hepatitis C virus (HCV) transmission to haemodialysis patients occurs by a route which remains to be clarified. Most studies show a significant correlation between anti-HCV-seropositivity and the number of blood transfusions or the duration of dialysis respectively. However, even in patients who have not received a blood transfusion the prevalence of HCV infection was significantly higher than in controls. We studied 58 patients on regular haemodialysis using a second-generation enzyme-linked immunosorbent assay (ELISA II) followed by a second-generation recombinant immunosorbent assay (RIBA II) for HCV. For all antibody-positive or indeterminate patients, polymerase chain reaction (PCR) analysis was done using both whole blood and dialysed ultrafiltrate. We were able to show by PCR that no HCV RNA (cells or cell particles) passed through the dialysis membranes.