Liver specimens of 31 autopsied cases of liver cirrhosis who had had detectable levels of antibody to hepatitis B core antigen (anti-HBc) inthe serum were stained for hepatitis B core antigen (HBcAg) and hepatitis B surface antigen (HBSAg) by the direct immunofluorescence method. Their premortem serum samples were tested for HBSAg, antibody to HBSAg (anti-HBS) and anti-HBC. Persistent hepatitis B virus (HBV) infection as judged by circulating and/or liver HB antigens was identified in 18 patients, and all of them revealed a high titer of anti-HBC ranging from 2(11) to 2(16) by the immune adherence hemagglutination method. In contrast, anti-HBC titer of the remaining 13 patients without detectable HB antigens was less than 2(9), and the geometric mean titer of anti-HBC of the patients with persistent HBV infection was significantly higher than that of the patients without (13.9+/-1.55 versus 7.23+/-1.30; t test, P less than 0.001). A combination of circulating anti-HBS and hepatic HB antigens was found in one patient, whose serum revealed an anti-HBC titer of 2(12). On the basis of these results, a high titer of anti-HBC in the serum (immune adherence hemagglutination titer of 2(11) or more) seems to be a reliable indicator of persistent HBV infection in the liver.