Electromagnetic flow measurement study was performed in 20 anesthetized dogs to evaluate the effect of selective celiac infusion of vasopressin on the hepatic arterial vasculature. Teh hepatic arterial flow showed a biphasic response with an initial decrease followed by a substantial increase in spite of a continued infusion. The left gastric, splenic, and superior mesentric arteries showed a monophasic response with persistent decrease of flow during the whole infusion. The biphasic response of the hepatic arterial flow is thought to be due to autoregulatory dilative action of the liver to a decrease of the portal flow. The results and previous clinical experience suggest that the selective infusions of vasopressin into arteries supplying the liver can be used for short-term vasoconstrictive therapy of acute gastrointestinal bleeding in patients without liver damage. Further experience is necessary to evaluate the safety of prolonged hepatic infusions in patients with liver damage.