We compared the presence of serologic markers of hepatitis B virus (HBV) infection with the presence of the viral DNA in the livers of patients with alcoholic liver disease with or without hepatocellular carcinoma. Among 51 patients with various kinds of alcoholic liver disease but without hepatocellular cancer, 19 had one or more serologic markers of HBV, but only three had viral surface antigen in their serum. These three patients, as well as three others who had HBV antibodies but no viral antigen in their serum and two others who had no serologic markers of any kind, had HBV DNA in their liver cells. In at least five of the eight patients with viral DNA in the liver, the DNA was integrated into the genome. Among 20 patients with alcoholic cirrhosis and hepatocellular carcinoma, nine of the 16 tested had serologic markers of HBV infection, but all 20 had HBV DNA integrated into the genome of the neoplastic liver cells. These data suggest that HBV plays a part in the pathogenesis of primary liver-cell cancer in alcoholics.