• Promethazine was given to 104 surgical patients under various conditions to test its possibilities in anesthesiology. It was administered either intramuscularly or intravenously in doses of 1 mg. per kilogram of body weight up to a total of 25 mg. in children or in total doses of 25 to 50 mg. in adults. These doses proved to be inadequate or unreliable as the sole preanesthetic medication, but increased the sleepiness in 38 out of 43 patients when given in addition to routine premedication such as morphine and scopolamine. Used in conjunction with meperidine and with or without chlorpromazine as a premedication in 25 children before diagnostic procedures, it caused all to fall asleep promptly and eliminated the need of supplementary anesthesia in 13. Evidence of usefulness in other situations was also obtained, especially in the prevention of postoperative nausea, vomiting, and excitement, and in the prolongation of the relief afforded by opiates in patients with malignancies. The doses required to produce these effects in man, when calculated on the basis of body weight, were much less than the doses found lethal to 50% of laboratory mice and dogs.