Immunological reactivity in alcoholic hepatitis has bben attributed to alcoholic hyalin, the histological hallmark of this disease. A purified isolate of alcoholic hyalin with electron microscopic, biochemical, and serological characteristics documented previously was added to lymphocytes from healthy subjects and patients with alcoholic hepatitis or other hepatic disorders. Production of migration inhibition factor (MIF) in response to this material was used as an index to lymphocyte reactivity. MIF was significantly increased in lymphocytes obtained from patients with alcoholic hepatis, as compared to the healthy controls (P less than 0.001), and persons with other liver diseases (P less than 0.005). These observations indicate that immunological hyperreactivity to alcoholic hyalin occurs in patients with alcoholic hepatitis; such activity may be of key importance in the pathogenesis or sequelae (or both) of this disease.