Differences in O2 delivery and consumption along the fed and fasted small intestine are described. Total wall blood flow was determined in sequential segments of small intestine from 5 to 6-month-old male, anesthetized Fischer 344 rats either 75-80 min before or after feeding, using radioactive microspheres. Oxygen saturation in submucosal arterioles and venules (50-60 micron diam) was determined throughout the intestine, using a microspectrophotometric technique. Venous O2 saturations showed considerable heterogeneity in all regions, and ranged from 0 to 77%. Arterial-venous O2 content differences (CaO2-CvO2) did not change along the fasted rat intestine, and averaged 8.2 ml O2/100 ml blood. However, CaO2-CvO2 followed a small proximal to distal gradient (proximal greater than distal) in the fed rats. Larger proximal to distal gradients (proximal greater than distal) occurred in both blood flow and O2 consumption in both groups. Feeding did not change intestinal average CaO2-CvO2. However, feeding induced a 53% increase in average O2 consumption, with the greatest increase (130%) occurring in the middle third of the intestine. Feeding induced a 42% increase in average blood flow, with the greatest increase (70%) occurring in the distal third of the intestine. The increased O2 used by the fed intestine was primarily provided by the increased blood flow. The O2 consumption gradient is assumed to reflect differences in mucosal mass along the intestine and/or differences in metabolic activity.