One hundred liver biopsies from 100 patients with clinical presumptive diagnosis of hepatitis were examined by immunofluorescence for the presence of hepatitis B surface antigen (HBSAg) and hepatitis B core antigen (HBcAg). Of the 60 HBsAg-positive livers, 51 were diagnosed as chronic hepatitis on histological grounds, 6 as acute hepatitis, and 3 as "near-normal liver." From the 60 tissue-positive cases, 3 subjects were HBsAg seronegative. HBcAg was detected in 44 livers, all of which also had HBcAg in the localized in the cytoplasm and the membranes of the hepatocytes, and HBcAg in the nuclei and in 4 cases also in the cytoplasm. Predominant HBsAg expression in the cytoplasm was observed in near-normal liver, chronic persistent hepatitis, and cirrhosis with little activity. This correlated with the amount of ground glass hepatocytes in the biopsies. HBcAg and membrane-localized HBsAg were minimal in those conditions. HBcAg was most prevalent in patients with chronic aggressive hepatitis and active cirrhosis treated with immunosuppressive drugs, whereas the amounts of HBsAg and HBcAg in nontreated patients of those two groups and in acute hepatitis with signs of transition to chronicity were almost equal. HBsAg expression in liver cell membranes was most prominent in active forms of chronic hepatitis (chronic aggressive hepatitis and in active cirrhosis) and in acute hepatitis with signs of transition to chronicity. This observation correlated in the presence of HBcAg in the biopsies of those patients. In acute hepatitis both HBsAg and HBcAg were detected rarely and no membrane expression of HBsAg was observed. The over-all results show a significant relationship between the different degrees of accumulation of HBsAg and HBcAg in the liver and the various histological types of hepatitis and further suggest an interplay of both hepatitis B virus and host immune response in the development and pathogenesis of hepatitis B.