The preparations of posterior pituitary extract are assayed for pressor potency on the basis of the effects observed on the blood pressure of the dog under chlorbutanol anesthesia. In the nonanesthetized animal, however, it has recently been shown that the intravenous injection of these preparations leads to quite variable blood pressure responses.1Since posterior pituitary extract is recommended for use in the treatment of shock and paralytic ileus in man, it is of interest to know how the pressor-assayed strengths of different preparations, as determined on the anesthetized animal, correspond quantitatively with the actions observed on the blood pressure and intestine when the complicating factor of the anesthetic is eliminated. Apart from this practical significance, such a comparison is of value in determining whether or not these effects of the extract are due to one and the same or to different constituents. In order to obtain the desired data,