We have developed a simple experimental model for studying reversible intestinal ischemia. The model is based on tenting the mesenteric vessels (artery and vein) to a tied loop of the small bowel in rat and, after a certain time, lowering them down again. Total and partial ischemia (created by tenting 2 and 1 cm, respectively) were demonstrated by laser Doppler flowmetry, as was the revascularization obtained after bringing the vessels down again. Alterations in mucosal permeability after ischemia were determined by depositing fluorescent dextran 3000 in the tied loop and measuring its concentration in the portal blood, and mucosal damage due to ischemia was assessed by measuring the activity of N-acetyl-beta-glucosaminidase, a lysosomal enzyme, in the gut lumen. There was a significant increase in the intestinal permeability to dextran 3000 after total ischemia for 10 min or more, and the permeability was directly related to the duration of the ischemia. After the intestine had been subjected to total ischemia for 30 min or more, the activity of N-acetyl-beta-glucosaminidase in the luminal contents was significantly increased. The permeability after partial ischemia for 30 min was less than that after total ischemia for 30 min. After total ischemia for 10 min followed by revascularization for 30 or 60 min, the permeability did not differ from that in animals not subjected to ischemia. It is concluded that this simple model may be used to study reversible small intestinal ischemia and factors that influence mucosal permeability.