The relationship of blood flow and oxygen uptake to ischemic intestinal injury was investigated by measuring the clearance of 131I-albumin from the blood to the lumen of isolated, perfused segments of canine jejunum. Reductions in blood flow for 2 h to various levels confirmed the previously demonstrated relationship of oxygen uptake to blood flow, i.e., oxygen uptake was flow-independent at blood flows above 30 ml/min · 100 g, and flow-dependent at levels below this. Blood flows above this threshold did not change the level of albumin clearance seen under control conditions (0.022 ± 0.003 ml/min · 100 g). However, increases in the mucosal permeability to albumin were seen after blood flow was reduced to levels where oxygen uptake was decreased by more than 50%. These findings indicate that the ability of the small intestine to maintain oxygen consumption during low flow states may be an important factor in providing protection from ischemic injury, even during prolonged periods of hypoperfusion. © 1985.