An analysis of the expression of the histocompatibility antigens in the livers of patients with chronic hepatitis B virus infection and normal subjects has demonstrated an increased expression of HLA-A,B,C antigens on the hepatocytes of patients with a low level of viral replication (HBe antibody positive) as compared with patients who exhibit a high level of viral replication (HBe antigen positive) and controls. This increase in the expression of histocompatibility antigens on the hepatocytes was associated with a decrease in the membrane expression of viral antigens by the same cells. These differences in the density of HLA and viral antigen display may influence the efficiency of T-cell cytolysis of hepatitis B virus-infected hepatocytes.