1. A group of 33 patients with mental diseases of whom 24 had schizophrenia, was treated with insulin intravenously. Twenty-three patients were treated with the intravenous injection of unmodified insulin and 10 patients with the intravenous injection of a solution of zinc-insulin crystals. Definite improvement was observed in 14 patients so treated. Of these, 4 patients relapsed within a period of two years following cessation of therapy.2. A solution of zinc-insulin crystals intravenously is recommended for use when patients are allergic to unmodified insulin; otherwise more favorable effects were obtained with the unmodified insulin.3. The intravenous method of insulin treatment has the advantage of producing comparatively rapid improvement in patients with mental disorders and requires less time daily for the period of therapy.4. A tendency to relapse was less marked when the patients were treated with intensive psychotherapy or when they were discharged to a favorable external environment.5. It is believed that intravenous insulin shock technique is the method of choice in the treatment of patients whose psychoses have developed acutely and are of short duration.