In order to clarify the relationship between hepatocellular carcinoma (HCC) and integration of hepatitis B virus (HBV) DNA into the host hepatocyte genome, the states of HBV DNA in 14 cases of HCC, 3 cases of chronic hepatitis, 2 cases of metastatic hepatic carcinoma and 4 normal livers were examined by the Southern blot hybridization technique. All 3 cases of HCC positive for serum HBsAg had both free and integrated HBV DNA. Integration of HBV DNA without free HBV DNA was detected in 2 cut of 4 HCC cases negative for serum HBsAg but positive for more than one of the HBV-related antibodies. Only free HBV DNA was observed in all 3 cases of chronic hepatitis positive for serum HBsAg. The remaining cases had no HBV DNA in their liver tissues.