It is well known that the responses of serum gamma glutamyl transferase (GGT) to chronic alcohol drinking are different depending on the individual. In order to clarify the genetic backgrounds in the development of alcoholic liver and pancreatic diseases, the relationships between serum GGT response and alcoholic liver and pancreatic diseases in heavy drinkers were studied. The responses of GGT to alcohol drinking were classified into three groups: non-response, mild-response and hyperresponse. In alcoholic liver disease, non-responders were scarcely found and the response of GGT tended to increase in parallel with the progression of liver disease, when the hepatitis C virus (HCV) marker-positive patients were excluded. The differences in GGT levels between just after and at 4 weeks after abstinence in the HCV marker-negative patients were significantly higher than those in the HCV marker-positive patients. The rate of decrease in GGT activities during 4 weeks following abstinence was significantly higher in the HCV marker-negative patients than in the HCV marker-positive patients, indicating higher GGT induction in the HCV marker-positive patients. All patients with alcoholic pancreatitis, but without liver disease, were non-responders. All patients, except one, with severe pancreatitis were also non-responders. In alcoholic pancreatic disease, GGT induction correlated negatively with the development of pancreatitis. These results suggested that genetic polymorphism of GGT may link with the induction of GGT by alcohol drinking, and consequently link with the development of alcoholic liver and pancreatic diseases.