The purpose of this study was to use a microdialysis technique to demonstrate the metabolic changes that occur in the intestinal wall during ischemia in vivo. Continuous monitoring of glucose, lactate, and glycerol using a microdialysis technique was performed in the jejunal wall of 10 pigs during steady-state and occlusive ischemia. The microdialysis catheters were introduced 50, 80, and 110 cm from the ligament of Treitz. Occlusive ischemia was established to two segments after steady state was reached. Microdialysate samples were collected from ischemic/nonischemic intestinal segments simultaneously every 20 minutes. For comparison with the microdialysis measurements, systemic blood samples were drawn from the cannulated femoral artery and analyzed consecutively. A significant increase of microdialysate lactate and a significant decrease of microdialysate glucose were found during occlusive ischemia as compared to the preischemic samples and samples from the nonischemic control catheters. The microdialysate glycerol increased during ischemia, but later than the lactate. No changes were observed in systemic serum lactate, serum glucose, pH, p co(2), and p o(2), but serum potassium increased by 1.1 mmole (median) during ischemia. Microdialysis measured in the intestinal wall identifies local ischemia and may be a new method for the monitoring of intestinal perfusion.