Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are closely involved in the mechanism of skeletal muscle ischemia/reperfusion (I/R) injury. This study was designed to determine the effects of inducible nitric oxide synthase (iNOS) inhibitor 1400 W on the reperfused cremaster muscle in extracellular super-oxide dismutase knockout (EC-SOD(-/-)) mice. The muscle was exposed to 4.5 h of ischemia, followed by 90 min of reperfusion. Mice received either 3 mg/kg of 1400 W or the same amount of phosphate-buffered saline (PBS, as a control) subcutaneously at 10 min before the start of reperfusion. 1400 W treatment markedly improved the recovery speed of vessel diameter and blood flow in the reperfused cremaster muscle of EC-SOD(-/-) mice compared to controls. Histological examination showed reduced edema in the interstitial space and muscle fiber, and reduced density of nitrotyrosine (a marker of total peroxi-nitrate (ONOO(-)) level) in 1400 W-treated muscles compared to controls. Our results suggest that iNOS and ONOO(-) products are involved in skeletal muscle I/R injury. Reduced I/R injury by using selective inhibition of iNOS perhaps works by limiting cytotoxic ONOO(-) generation, a reaction product of nitric oxide (NO) and super-oxide anion (O(2) (-)). Thus, inhibition of iNOS appears to be a treatment strategy for reducing clinical I/R injury.