We measured serum aspartate transaminase (AST) concentration and serum hepatitis B virus (HBV) DNA concentration in homosexual men with chronic HBV infection and a spectrum of immune deficiency as a result of exposure to human immunodeficiency virus (HIV). Serum AST and HBV DNA concentrations were similar in patients with varying immune function as indicated by in vivo criteria (diagnosis and skin tests reactivity) and in vitro criteria (lymphocyte transformation responses to mitogens and Candida and tetanus antigens) and were unrelated to the number of circulating T cells, suppressor/cytotoxic cells, helper cells, natural killer cells, and the helper:suppressor ratio. Serum AST concentration and indices of cellular immune function were similar in patients with varying HBV replicative activity (high and low HBV DNA concentrations). The observed lack of relationship between serum AST concentration and indices of cellular immune function and HBV replication suggests either that other factors determine the severity of hepatic inflammation in chronic HBV infection, or that currently available tests of cellular immune function and HBV replicative activity do not accurately reflect processes in the liver.