1. In 30 out of 35 insulin experiments the post-sugar delta index is considerably less than the pre-insulin delta index. In about this same proportion of cases patients show clinical improvement after treatments.2. Mean delta indices for 37 normals are 2.1 cm., extremes 0.5-11.0 cm. Thirty-four of these were 3.2 cm. or less, the three higher values were 5.0, 6.0, and 11.0 cm. One normal awake gave a value of 0.5 cm.; asleep 10.9 cm. Twelve chronic alcoholics gave a mean of 2.5, extremes 0.5-6.0 cm. Nine manic depressives gave a mean at 2.8, extremes 1.0 to 5.2. Thirty-one untreated schizophrenics gave a mean of 6.6 cm., extremes 0.5 to 25.2. Twelve of these values were greater than the schizophrenic mean of 6.6 cm. Despite the mean differences the delta index cannot be regarded by itself as a measure of the schizophrenic state owing to overlaps in values between the groups of normals and patients.3. Eighty-four delta indices taken on seven patients showing high pre-treatment indices, each over some weeks of treatment, exhibit in 88 per cent of the case complete correspondence with independently determined, fluctuating, objective clinical symptoms. With two other patients indices corresponded to symptoms in 60 per cent and 70 per cent of the instances. These two patients were verbally unresponsive and showed little detectable day-to-day change in symptoms to correlate with the indices. Patients who have "low" pre-treatment delta indices, i. e., 4 cm. or less, about 50 per cent of a group of 31, cannot, of course, be analyzed by this method.4. In schizophrenic patients we have found no special brain waves qualitatively different from those found in normal persons.5. Transient relapses and remissions of one patient, earlier released after apparently successful insulin therapy, correlated completely with very specific fluctuations in his delta index.6. In nine instances, with several patients, delta indices have been found to change prior to any other objective change in symptoms. Five of these nine prognostic changes were recorded with one individual.Abstract Teaser