Abstract Portal venous pressure, portal venous oxygen saturation, portal blood flow, and total hepatic blood flow have been studied in anesthetized dogs given single or repeated injections of surgical Pituitrin and in dogs given a continuous infusion of Pituitrin. Following a single injection of surgical Pituitrin a prompt, marked, but transient decrease in portal flow occurs. A similarly prompt, marked, but somewhat more sustained decrease in portal pressure is noted. The saturation of the portal venous blood falls. Hepatic blood flow decreases somewhat less than portal blood flow and the response is even more brief. Similar responses are observed repetitively when repeated injections of Pituitrin are given. With the continuous infusion of Pituitrin, portal blood flow drops to a low level and is maintained. A similarly sustained decrease in portal pressure is noted. Hepatic blood flow falls immediately but soon afterward rises to a level within 30 per cent of the normal value. A negligible increase in arterial blood pressure accompanies the infusion of Pituitrin. The difference in the response of the portal and of the hepatic blood flow to the infusion of Pituitrin is interpreted on the basis of the contribution of hepatic arterial inflow into the liver. These observations suggest that during the infusion, hepatic vascular resistance decreases with a concomitant increase in hepatic arterial inflow. The experimental observations suggest the desirability of continued exploration of the potential usefulness of infusions of Pituitrin in the management of patients with bleeding esophageal varices.