The prevalence of hepatitis C infection was evaluated (Ortho HCV Antibody ELISA Test) in 64 patients with chronic renal failure treated in a single hemodialysis unit. None of these patients was a carrier of hepatitis B virus nor of antibodies against human immunodeficiency virus. Antibodies against hepatitis C virus were detected in 11 patients (17%). The prevalence was higher in the 13 previously diagnosed of non A, non B hepatitis (77%) than in the 51 without previous hepatitis (2%) (p less than 0.001). A relationship between the infection rate and the number of previous blood transfusions was also observed: 5% in the patients without previous transfusions, 13% in the 30 patients who had received between 1 and 10 blood units and 40% in the 15 who had received more than 10 blood units (p less than 0.05). These data suggest that the hepatitis C virus may be responsible for most episodes previously diagnosed as non A, non B hepatitis, and that blood transfusions are the major risk factor.