Skeletal muscle is very sensitive to ischemia. A prolonged preoperative ischemic interval decreases the chances for successful replantation of an amputated limb. Recent experimental work has implicated toxic oxygen free radicals produced during reperfusion of ischemic tissue to be responsible for some of the observed deleterious cellular changes. Selected oxygen free radical scavengers have been used to increase skeletal muscle survival following total ischemia. This study examined the effect of systemic administration of a superoxide free radical scavenger, superoxide dismutase (SOD), and a hydroxyl radical scavenger, dimethylsulfoxide (DMSO) just prior to reperfusion, on the ultrastructure and function of ischemic rabbit anterior tibialis muscle.White male New Zealand rabbits were used for this study. The right hind limb of each rabbit was made ischemic by dissecting and clamping the femoral artery and vein proximal to the bifurcation of the profundus artery and vein. A penrose tourniquet was also placed around the knee. The animals were divided into groups subjected to either 5 or 8 hours of ischemia.