The development of a serologic assay to detect antibodies directed at an antigen (C-100-3) of the hepatitis C virus (anti-HCV) has been a major breakthrough in the long search for causative agents of non-A, non-B (NANB) hepatitis. The frequency of HCV in those who have end-stage liver disease is not known. Moreover, the rate of recurrence after liver transplantation (OLTx) and the rate of acquisition of new HCV infection as a result of the OLTx experience is as yet unknown. This study was performed in an attempt to answer these questions. The prevalence of HCV in 372 patients undergoing OLTx at the University of Pittsburgh was determined. Those transplanted for HBV-related liver disease with hepatoma had the highest rate of HCV antibody positivity (45.4%) followed by those with metabolic liver disease (42.5%), putative NANB liver disease (41.4%), and cryptogenic cirrhosis (20.9%); those with cholestatic liver disease exhibited the lowest rate (16.2%). HCV antibody was positive in only 26.3% of patients with hepatoma. Of those patients who were negative prior to transplantation, 12.2% acquired HCV antibody post-OLTx. In the putative NANB group, no difference was detected in the AST and ALT prior to transplantation in either the HCV antibody-positive or -negative patients. In patients with cryptogenic cirrhosis, those who were positive for HCV antibody had higher transaminase levels prior to transplantation than did those patients who were HCV antibody negative.