1. The majority of schizophrenic patients who improved clinically, showed a significant change in their oral glucose tolerance, this change being towards the normal.2. In the occasional case, clinical improvement did occur without any significant change in the glucose tolerance.3. Those who did not improve or deteriorated clinically, showed no change in their abnormal tolerance or it became more abnormal.4. This change could not be attributed to the administration of insulin per se, nor entirely to the change in absorption of the glucose in the gastro-intestinal tract.5. The pre-treatment glucose tolerance curves in this series of schizophrenics, seem to show an abnormally prolonged period before the return to fasting levels.