Chronic alcohol consumption leads to increased activities of gamma-glutamyltransferase (GGT) in the serum which are associated with an enhancement of GGT activities in the liver. These findings suggest that increased GGT activities commonly found in alcoholic liver disease can be ascribed primarily to hepatic enzyme induction rather than to liver cell injury, since hepatic GGT activities were increased but not reduced. Moreover, at the fatty liver stage the fetal form of GGT in the serum is much higher in activity that the adult form, whereas the reverse constellation can be found in patients with alcoholic liver cirrhosis. Thus, these preliminary data suggest that the determination of various forms of GGT in the serum of alcoholics may be useful in establishing the particular stage of alcoholic liver disease by a simple enzyme test in the serum.