Two hundred patients received promazine in dosages of 50 mg. to 1.5 gm. daily for two to six months. They ranged in age from 22 to 72 years and had been mentally ill from one to 15 years. Promazine diminished violence and acute overactivity, and reduced combativeness and distortion of sense perceptions. Relapses were common on cessation of treatment. Promazine alleviated insomnia, incldding patients in whom sleeplessness was believed to be the result of arteriosclerosis. It incrased emotional control, improved interpersonal relationships, reduced active antagonism, but left fixed paranoid delusional ideation mostly unaffected. There was less constraint, and there was increased verbalization among the withdrawn, intellectually preserved types of patient. Little change was seen in moderately deteriorated patients with apathy and defective judgment. The deeply regressed, severely disturbed or vegetative patients showed some improvement, particularly in bladder and bowel control. Of the 200 patients treated, 15 (7.5 per cent) were released; none had returned after three months. There were no side effects detected on clinical or laboratory examination. Drug habituation to promazine was not evident.