Hepatitis C virus (HCV) infection has recently become the major cause of chronic liver disease among patients on chronic hemodialysis. The use of erythropoietin for treatment of anemia has reduced the number of blood transfusions, but the frequency of HCV infection has not declined in hemodialysis units. The exact mode of transmission of HCV within dialysis units is as yet incompletely defined, but there is evidence to support nosocomial transmission by sharing dialysis machines in the hemodialysis unit. We performed a study to estimate the prevalence of HCV infection in our hemodialysis unit and to evaluate the effect of patient isolation and use of devoted dialysis machines for HCV-positive patients on the spread of HCV infection. A total of 168 patients on chronic hemodialysis (92 males and 76 females; mean age 54 +/- 12) were screened for HCV-antibodies (HCV-Ab) before their admission to the dialysis unit. Seropositive patients were isolated and confined to dedicated dialysis machines. Aminotransferases were measured monthly and HCV-Ab screening was performed second or third generation ELISA test every two months. Seropositive patients were tested by the PCR for the detection of HCV-RNA. Between March 1992 and August 2000, eight of 168 patients showed seroconversion. Seropositive patients were also found HCV-RNA positive. Four of these patients have become seropositive after they had undergone hemodialysis in other dialysis centers on holiday, two patients had received blood transfusions within the six months preceding seroconversion. The prevalence of HCV positivity in our hemodialysis unit is 4.7%. The low prevalence of HCV infection of our unit suggests that patient isolation and use of dedicated dialysis machines for seropositive patients decrease the transmission of HCV infection in hemodialysis units.