Specimens of liver tissue obtained by biopsy from five patients and at necropsy from seven patients with postnecrotic liver cirrhosis and hepatocellular carcinoma were examined for the presence of hepatitis B surface antigen (HBs Ag) and hepatitis B core antigen (HBc Ag) by direct immunofluorescence. In all cases, samples of serum were tested for HBs Ag and antibody to HBs Ag (anti-HBs) by immunoelectroosmophoresis and for antibody to HBc Ag (anti-HBc) by indirect immunofluorescence. Of these 12 representative cases of the main histological types of hepatocellular carcinoma, six were found to be seropositive for anti-HBc, and three of them were negative for HBs Ag. HBs Ag was detected in the cytoplasm of hepatocytes in the cirrhotic nodules in one seronegative patient and in three of the seropositive cases. In the latter cases, HBs Ag was identified in the cytoplasm of cells in well-differentiated hepatocellular carcinoma. HBc Ag was not found in any of the specimens examined.