To assess possible geographical differences in the spread of hepatitis-C virus (HCV), the prevalence of antibodies against HCV (anti-C-100-3) was investigated in various adult population groups in 29 centres in Italy. Anti-HCV was positive in 375 out of 28,433 voluntary blood donors (1.3%): prevalence was higher in southern Italy (1.51%) than in the northern regions (1.28%), but the difference was not statistically significant. Anti-HCV prevalence was similar in the north and south in post-transfusion chronic hepatitis (91%), haemophiliacs (73%), intravenous drug users (70%), and haemodialysis patients (28%), where parenteral contacts are obvious, and in HBsAg carriers (14%), a group with evidence of previous parenteral contamination. In contrast, anti-HCV prevalences were found to be significantly higher in the south than in the north and central Italy among patients with hepatocellular carcinoma (HCC) (73 vs 59%), cryptogenic liver disease (67 vs 58%), autoimmune chronic hepatitis (72 vs 44%) and alcoholic liver disease (51 vs 34%). These results indicate a very high circulation of HCV in Italy, with maximum incidence in the south and in the islands. They suggest that its spread in the community can occur through inapparent parenteral routes as observed for hepatitis-B (HBV) and hepatitis-delta viruses (HDV) and possibly facilitated by poorer social-demographic and life-style factors.