We determined superoxide radical in ischemia-reperfu-sion to skin flaps by electron spin resonance and observed itseffect to skin flap survival. The experimental results showthat superoxide radical arise in ischemia-reperfusion. By per-fusion with superoxide dismutase,as free radical scavengers,significantly improved flap survival rate over controls. Basedon experimental date, the pathology mechanisms of skin flapnecrosis is discussed.