Blood flow, arteriovenous O2 difference, and lumen pressure were measured in isolated loops of canine ileum. Ileal pressure was increased by an intra-arterial infusion of either Met-enkephalin or acetylcholine. Pressures were quantitated using a motility index (MI = mean of the pressure peaks divided by number of contractions per minute). Both Met-enkephalin and acetylcholine increased MI in a dose-dependent fashion. The highest MI achieved with acetylcholine was 37.9 mmHg, while Met-enkephalin produced a maximal MI of 8.1 mmHg. Ileal oxygen uptake increased when MI reached values greater than 6. There was a direct linear relationship between oxygen uptake and MI. Distension of the lumen in the absence of motility resulted in a decrease in oxygen uptake when lumen pressure reached 15-20 mmHg. The results of these studies indicate that contractions of intestinal smooth muscle can increase intestinal oxygen uptake and may contribute to the overall oxygen demands of the gut under conditions of fasting and feeding. Furthermore, large (greater than 20 mmHg) increments in lumen pressure during enhanced motility may compromise intestinal oxygenation.