The present study deals with possible connections between the schizophrenic syndrome and alterations of the glucose-insulin metabolism. Data have been obtained in 18 patients, 9 males and 9 females, aged 22-62 years, suffering from chronic schizophrenia of 5-29 years duration. The patients were treated with Haloperidol for 30 days, 6 mg, i.m.p.d. to a total dose of 180 mg. The glucose metabolism was examined through a GTT (with a glucose load of 100 gr. per os), and an Insulin Tolerance Test (with 0.1 U/kg body weight). The insulin levels were examined under glucose load by the radioimmunological assay of Hales and Randle. The glycemic levels were examined under glucose load by an oxidative method. The psychopathological features were controlled by a Wittenborn Rating Scale. The metabolic and psychological examinations were done twice before the beginning of therapy, at 46 hrs. interval, then at 10-20-30 days of therapy. The results are probative for the presence of a chemical diabetes in a significantly high percent of patients. The significance of possible neurotransmitter impairments acting at both the biochemical and psychological levels is discussed.