The posterior lobe of the pituitary gland contains 2 active principles, [alpha]-hypophamine, which contracts uterine muscle and [beta]-hypophamine, which raises blood pressure. It was a question whether the well-known diuretic-antidiuretic action of pituitary extracts was due to one of these principles or to a 3rd. Experiments were made upon rabbits under urethane, amytal, chloral-hydrate and chloretone anesthesia. The rate of flow of urine was determined by counting the number of drops falling from a cannula in the bladder. The intravenous injection of [alpha]-hypophamine had little effect upon the flow of urine whereas [beta]-hypophamine, caused first a decrease in urine flow, then a copious flow lasting a few min., followed by a decreased output. The intensity and duration of these effects varied in different rabbits and seemed to depend upon the depth of anesthesia and upon the dosage of pressor principle. Renal function tests were made which showed that the oxytocic principle had little effect upon the excretion of dye whereas the pressor principle diminished the rate.