Fifty-one patients with signs of past HBV infection were investigated for the HCV virus antibody. All patients were at least HBsAb, HBcAb positive. Two groups were selected: patients with increased serum AST activity (32/51) and patients with normal serum AST activity (19/51). Prevalence of HCV infection was higher (81.2%) in the group with high serum aminotransferases as compared to that found in the second group (31.6%) (p less than 0.002). Furthermore, histological findings showed higher prevalence of HCV infection in patients with cirrhosis as compared to patients with hepatic fibrosis. Results show that lack of clinical remission in patients with past HBV infection could be due to the presence of HCV, thus representing an unrecognized cause of "cryptogenetic" liver diseases.