Response of hepatic arterial and intrahepatic portal venous vasculature to 10-min infusions of either isoproterenol or epinephrine was studied in 37 in situ dog liver preparations. Isoproterenol infusions at various dose rates (3.06–24.45 µg/min) were given by way of hepatic artery or portal vein. Hepatic arterial vasodilation, which was abolished by propranolol, was clearly evident while response of intrahepatic portal venous bed was incon sistent and not indicative of significant vasodilation. Arterial dilator response was attenuated later in the infusion period when isoproterenol was given at high dose rates. Femoral venous infusions of epinephrine (9.55 µg/min) resulted in a variable and slight hepatic arterial response while portal resistance was consistently increased. Following sotalol, epinephrine produced a marked increase in hepatic artery resistance in every case while intrahepatic portal venous resistance was increased to the same extent as before. It was concluded that both α-receptors (constrictors) and β-receptors (dilators) are present in canine hepatic arterial and mesenteric vessels while intrahepatic portal venous vasculature appears to possess few, if any, β-receptors.