To examine the relationship between hepatitis B core antigen-specific interferon gamma production and the liver injury, we measured the sequential change in this production by peripheral blood mononuclear cells of seven patients with chronic hepatitis B. Four patients who experienced acute exacerbation showed increased interferon gamma production when the serum alanine aminotransferase level peaked or during the recovery phase. In the three patients who did not experience acute exacerbation, interferon gamma production gradually decreased in one who had a low peak of alanine aminotransferase but did not show significant change in the other two. Increased production of hepatitis B core antigen-specific interferon gamma at the time of acute exacerbation suggests that interferon gamma induced by hepatitis B core antigen plays a role in hepatocellular injury of patients with chronic hepatitis B.