The specific susceptibility of the intestinal mucosa to low blood flow states is related to the "physiologic" makeup of the intestinal milieu. Pancreatic proteases appear to play a crucial role in the ischemic autodigestion of the intestinal mucosa. Moreover, trypsin can activate the conversion of xanthine dehydrogenase into superoxide radicals producing xanthine oxidase. Oxygen-derived free radicals account for at least part of the damage to the postischemic intestinal mucosa.