Ischemia-reperfusion injury remains a difficult problem facing vascular surgeons because of its associated high morbidity and mortality. The basis for tissue injury during ischemia depends on depletion of tissue oxygen and energy substrates. Cell injury, as documented cellular edema and lysosomal degranulation, begins after only 30 min of ischemia. Irreversible cellular changes occur after 4-6 h of skeletal muscle ischemia. Following acute arterial occlusion, the restoration of blood flow heralds the onset of biochemical events, forming the basis of what is known as the reperfusion syndrome. This tissue injury is maximal in areas with the greatest blood flow during reperfusion. Endothelium-leukocyte interactions play an important role in ischemia-reperfusion injury. Both endothelial and white blood cells have the biochemical machinery and capacity to generate molecular signals, to express adhesion proteins, and to produce toxic metabolic by-products. Since the microcirculatory changes in ischemia-reperfusion injury parallel those seen in inflammation, the leukocyte-endothelial interaction can explain many of the reactions associated with the early phases of ischemia-reperfusion injury.