The prevalence and incidence of hepatitis C virus (HCV) infection in a hemodialysis unit were assessed during a two-year period. Until May 1991 the serological test employed was a first-generation ELISA; since that date second generation tests (ELISA and RIBA) have been used. The first serological survey, undertaken in December 1989, showed a 17 % prevalence of anti-HCV antibodies. This had increased to 29 % in the survey of November 1991. During the study period ill patients had been receiving hemodialysis in our unit, 24 of them showing positive tests for HCV Eleven of these were positive in December 1989, 4 were false positive with the first generation ELISA test; 4 were seropositive on admission to our unit and the other 5 became infected within the dialysis unit - one transfused before HCV screening became mandatory in May 1990 and the other 4 with nosocomial transmission. The incidence of nosocomial infection has been 27 cases/100 patient-years and has become the most important route of infection.