168 HBAg seropositive and 105 HBAg seronegative liver biopsies were studied for correlations between anti-HBc titers (indirect immunofluorescence method) and tissue expression of HBsAg and HBcAg (immunofluorescence), Dane particles in blood (immune electron microscopy) and inflammatory reaction. 98.8% of the HBAg seropositive patients were positive for anti-HBc. The mean titers showed statistically significant differences mainly between chronic aggressive hepatitis (1:2(11.3)) versus lobular hepatitis (1:2(10.1)), chronic persistent hepatitis (1:2(9.9)) and nonspecific reactive hepatitis (1:2(7.6)). Due to the considerable deviation of titers within the histological groups, however, titers below 1:2(11) are of low diagnostic relevance, whereas titers above 1:2(12) are mainly indicative of chronic aggressive hepatitis, although acute lobular hepatitis with signs of possible transition to chronicity or chronic persistent hepatitis with strong inflammatory activity may occur. Among HBAg seronegative patients 20% were positive for anti-HBc (mean titer = 1:2(7.7)). Among 78 patients also tested for anti-HBs, 10.2% were positive for both anti-HBc and anti-HBs. In an additional 12.8%, anti-HBc was the only marker of past hepatitis B virus infection. Anti-HBs was the only marker in a further 33%. In none of the HBAg seronegative patients and in only 59% of all HBAg seropositive patients, there was an association of anti-HBc with complete virus synthesis as measured by the demonstration of HBcAg in tissue or Dane particles in blood. It is concluded that anti-HBc is not a criterion of infectiosity but a specific, although non-characteristic, marker for HBAg seropositive acute and chronic hepatitis as well as for terminated HBV infection of all possible inflammatory and HBAg expression types.