1. Simultaneous observations of clinical symptoms, cerebral oxygen utilization, blood sugar level and electrical activity of the brain were made on patients with schizophrenia receiving the insulin treatment.2. Blood sugar decreases during the first hours after the injection of insulin and then remains at a low level until termination with sugar while the clinical signs continue to develop progressively throughout the entire course of hypoglycemia.3. The march of the symptoms is correlated with a gradual decrease of cerebral oxygen uptake and the electrical changes.4. The regression of the symptoms is accompanied by a gradual increase of the oxygen uptake and a reduction of the delta index. The sequence of the symptoms during regression is in an order which is the reverse of their appearance.5. During hypoglycemia the alpha waves disappear approximately at the time when the functions of the cortex are completely suppressed and reappear with the restoration of cortical functions.6. It is therefore, concluded that as a result of the hypoglycemia caused by the administration of insulin the metabolism of the brain is diminished. This reducton of cerebral metabolism is the cause of the clinical symptoms as well as the alterations of the cerebral electrical activity of the brain.7. These conclusions concerning the correlations between the clinical and physiological changes are to be regarded only as a working hypothesis because of the small number of the experiments performed.