Potential risk factors for the development of hepatocellular carcinoma were analysed in 40 Caucasian patients with this malignancy. A higher proportion (14 of 40; 35%) had evidence of hepatitis C virus (HCV) infection than had evidence of either hepatitis B virus (HBV) carriage (17.5%) or alcohol abuse (30%). In all 14 patients whose sera were reactive by HCV ELISA (Ortho second generation test), the presence of antibodies to HCV were confirmed by recombinant immunoblot assay (Ortho RIBA-2). Furthermore, two independent laboratories detected HCV-RNA in 10 of the 14 (71%) anti-HCV positive sera. Two additional sera were shown to contain HCV-RNA when reanalysed by a modified PCR using oligonucleotide primers designed to amplify a shorter fragment of the 5' noncoding region of the genome. Seven of the anti-HCV positive patients also had evidence of prior HBV infection and 2 admitted to alcohol abuse. HCV infection was the only identifiable risk factor in 6 patients. These data confirm the association between HCV infection and hepatocellular carcinoma and suggest that persistent viral replication accompanies tumour development in the majority of patients whose serum contains anti-HCV.