Hepatitis C virus (HCV) infection was studied in 60 liver transplant recipients. Antibodies to HCV were tested by both a second-generation ELISA test and a four-recombinant immunoblot assay (4-RIBA) just before the transplant and every three months thereafter. HCV RNA detection was performed by polymerase chain reaction (PCR) at least three times after the transplant in all the patients. Thirty-nine patients tested negative by ELISA before LT (group A), 14 patients tested positive by both serological tests (group B), and seven tested positive only by ELISA (group C). Posttransplant hepatitis was diagnosed in 11/14 in group B in comparison with 3/39 in group A (P < 0.001) and 1/7 in group C (P < 0.05). HCV RNA was detected in the sera of 14/14 patients in group B but in only 1/7 in group C and 6/39 in group A. Only 2/15 patients developed posttransplant hepatitis in the absence of HCV RNA detection. These data suggest that HCV is the major cause of hepatitis after LT. Patients HCV seropositive by RIBA test before the transplant formed a group of high-risk patients for developing viremia and hepatitis afterwards.