The fate and significance of hepatitis C virus (HCV) infection after renal transplantation (TP) remain debated. We therefore evaluated the incidence and outcome of HCV infection in 120 kidney graft recipients both at the time of TP and 54 +/- 28 (13 to 123) months later using ELISA-II and RIBA-II immunoblot. Furthermore, the presence of anti-HCV antibodies at follow-up was correlated with HCV viremia, as detected by the nested polymerase chain reaction (PCR), and with chronically abnormal ALT levels. At the time of TP, 17 patients (14.2%) had anti-HCV antibodies. Compared to anti-HCV (-) patients, anti-HCV (+) patients had a longer duration of pre-TP dialysis (P < 0.001) and had received more pre-TP blood transfusions (P < 0.01). After an average follow-up of 48.5 +/- 24.7 (21 to 97) months, all these patients remained anti-HCV (+) but only 10 were still RIBA "reactive" due to the loss of reactivity against the 5-1-1, C100 and C33 (but not the C22) antigens. Five initially anti-HCV (-) patients had become (+) at follow-up. Among the 22 patients anti-HCV (+) at follow-up, 20 had HCV-RNA detectable by PCR but only 10 had elevated ALT. Ten out of 13 HBsAg (-) patients with elevated ALT were anti-HCV (+). Our study indicates that disappearance of ELISA-II anti-HCV antibodies is rare in kidney recipients and that HCV infection may also occur after TP. Anti-HCV antibodies are likely to reflect a persisting infection as suggested by the frequent detection of HCV-RNA.(ABSTRACT TRUNCATED AT 250 WORDS)