Background: The mechanism responsible for the initiation and perpetuation of alcoholic liver disease (ALD) remains poorly understood. This investigation attempted to elucidate the role of cell-mediated immune phemonena in the pathogenesis of ethanol-induced liver injury. Methods: Frozen liver biopsy specimens from 144 patients with moderate to severe ALD were examined by the avidin-biotin immunoperoxidase technique for the expression of antigenic markers of T and B lymphocytes, natural killer cells, and class I and II MHC molecules in the tissue. Results: Expression of CD3 by lymphocytes correlated significantly with regenerating nodules, intralobular inflammation, central sclerosis, and abnormalities of Kupffer cells. B cells were rarely present, and natural killer cells were absent. CD3+ lymphocytes expressed either CD4 or CD8 surface molecules. Enhanced class I MHC expression correlated significantly with portal inflammation, limiting plate erosion, vascular abnormalities, and hemosiderosis. Expression of class II MHC molecules correlated significantly with necrosis, bile stasis, and Mallory bodies. Conclusions: The distribution and persistence of CD4+ and CD8+ cells in actively advancing ALD, the enhanced MHC expression on hepatocytes, and their relationship to alcoholic hyalin and necrosis lend support to the hypothesis that a cytotoxic T lymphocytehepatocyte interaction plays a role, perhaps via lymphokine production, in the genesis or perpetuation of ALD.