Sera from 130 renal transplant recipients were tested for antibody to hepatitis C virus (anti-HCV). Anti-HCV was detected in 6.2% of patients: 15.4% of patients who had maintenance hemodialysis (HD) and 2.2% of those who had continuous ambulatory peritoneal dialysis (CAPD) before transplantation (P less than 0.05). The similarity in prevalence of anti-HCV with patients currently on dialysis and the absence of transfusion during posttransplant follow-up suggest that most patients acquired HCV infection through transfusion during dialysis. The proportion of anti-HCV-positive patients who had one or more episodes of elevation in serum transaminase level was similar to that of hepatitis B surface antigen (HBsAg)-positive patients, 75% vs. 72.2%. However, anti-HCV was only detected in 25% of HBsAg-negative patients who had recurrent elevations in serum transaminase level. It is not clear whether the low prevalence of anti-HCV in these patients is related to the presence of other non-A, non-B hepatitis virus (es) or a decrease in titer of anti-HCV secondary to immunosuppression posttransplantation.