To determine whether a sensitization to ethanol metabolites occurs in alcoholic liver disease, reactivity of lymphocytes to nontoxic amounts of acetaldehyde was studied by direct elaboration of migration inhibitory factor (MIF) production. Eighteen alcoholics with various degrees of biopsy-proven liver damage showed increased MIF production in response to acetaldehyde; the mean value of the group differed significantly from 15 healthy controls, 15 subjects with nonalcoholic liver disease, and 15 alcoholics without liver involvement (P less than 0.001, P less than 0.001, P less than 0.02, respectively). Among the alcoholics with liver disease, none individuals (50%) with histological signs of advanced alcoholic hepatitis showed the highest percentage of inhibition of migration; the value differed significantly from the remaining patients with lesser degrees of hyaline necrosis in liver biopsies (P less than 0.005). These results indicate that acetaldehyde is involved in the pathogenesis of alcoholic hepatitis. Clinically, this test might facilitate the selection of patients with alcoholic hyaline necrosis.