This study examines the mesenteric blood flow response to feeding of newborn piglets. Experiments were performed in 21 term piglets age 4 hours to 4 weeks anesthetized with 0.25-0.75% halothane in O2 (depending on age) paralyzed with decamethonium bromide and ventilated artificially to maintain normal arterial pH, pCO2, and hydrated by 5% dextrose in 1/3 physiologic saline. The superior mesenteric artery flow was measured by electromagnetic probes. Arterial pressure, electrocardiogram and rectal temperature were simultaneously recorded. The stomach was intubated through the esophagus. Feeding in 10 or 15 ml increments (total amounts 23-27 ml/kg) of water or modified cow's milk elicited a 30-35% increase in mean mesenteric flow from the control values ½-1 hour postprandially in 7 piglets, 15-30 days old. Piglets under 2 days old showed the following flow changes from control values: an immediate but unsustained increase (10-30%) with water feed (8 cases); 5-12% decrease with modified cow's milk (3 cases) and 10-16% increment with sow's milk (3 cases) ½-1 hour after feeding. It is suggested that superior mesenteric blood flow response to feeding is age related.