Celiac and superior mesenteric arterial blood flows were measured simultaneously in conscious beagle dogs. The responses to food were completely different between the two arteries. Celiac flow increased quickly to 180-200% of the control 2 min after food but started to decline rapidly to preprandial levels, though greater than 90% of food was still in the stomach. It remained at preprandial levels over the next 1-6 h. Superior mesenteric flow increased gradually in 20-50 min (peak: 230%) and remained above the control levels for 3-6 h. The celiac response was inhibited by vagal block, hexamethonium, and gastric mucosal anesthesia by oxethazaine but not by atropine, phenoxybenzamine, or propranolol. Postprandial superior mesenteric hyperemia was blocked by mucosal anesthesia and was reduced by atropine by 80%. Ganglionic or adrenergic blockades were without effect. It is concluded that the celiac peak response to food is mediated by a nonadrenergic, noncholinergic vagal reflex in conscious dogs. Extrinsic nerves probably play little part in the postprandial increase of superior mesenteric flow.