n = 10); and (2) animals subjected to 3 hours of bilateral hind limb ischemia followed by reperfusion (n = 10). Both groups were observed under standard conditions for 4 days. In a second experiment three groups of animals were studied: (I) control (n = 12); (II) 3 hours of bilateral hind limb ischemia alone (n = 12); and (III) 3 hours of bilateral hind limb ischemia followed by 2 hours of reperfusion (n = 12). Animals subjected to bilateral hind limb ischemia followed by reperfusion had a significantly higher mortality rate (70%) than controls (0%) (p < 0.005). Morphometric assessment of the small bowel showed a significant decrease in mean mucosal thickness in the ischemia-reperfusion group compared with that in the group of controls and the ischemia-alone group (p < 0.05). Bilateral hind limb ischemia followed by reperfusion was associated with significantly increased plasma concentrations of endotoxin (p < 0.05) and interleukin-6 (p < 0.0001) compared with that of controls and ischemia alone. These results indicate that reperfusion of the acutely ischemic lower limb is accompanied by structural changes in the gut mucosa associated with increased systemic endotoxin concentrations and cytokine activation. Mortality following reperfusion of the acutely ischemic limb may be related to a systemic inflammatory response triggered by endotoxin of gut origin.