To investigate the role of lymphocytes frequently observed in the parenchyma of alcoholic liver disease (ALD), lymphocytes infiltrating into the liver were stained immunohistochemically with monoclonal antibodies (MoAb) and were quantitatively assessed by a morphometric analysis in 17 patients with ALD and, for comparison in five patients with chronic active hepatitis B (B-CAH). In patients with alcoholic hepatitis, the number of CD8+ lymphocytes in the hepatic lobule was similar to that in patients with B-CAH but was significantly greater than that in alcoholics with hepatic fibrosis (HF). The CD4/CD8 ratio in the hepatic lobule was low in both alcoholic hepatitis and B-CAH compared with that of alcoholic patients with HF. When Mallory bodies (MB) and lymphocytes were simultaneously stained with a specific antibody against MB and MoAb, respectively, only CD3+ and CD8+ lymphocytes were found to have a close contact with MB. These results suggest that in alcoholic hepatitis, hepatocyte necrosis may be partly mediated by immunological mechanisms involving cytotoxic T cells infiltrating into the hepatic lobule.