The mechanism of cocaine-induced rhabdomyolysis and/or muscle damage has not been elucidated. To determine if cocaine has a direct effect on muscle, isolated soleus and EDL muscles were incubated in the presence of 1 mM and 0.2 mM cocaine using a pulse and continuous exposure protocol. The release of creatine kinase from the isolated EDL muscle was statistically significant only when muscles were exposed to 1 mM cocaine for a period of 30 minutes. These findings suggest that cocaine-induced creatine kinase release could be mediated by a direct action on the fibers. It is also possible, however, that cocaine-induced muscle damage and creatine kinase release may be mediated via an indirect effect. It is possible that cocaine's vasoconstrictor effects could lead to muscle damage via an ischemia-reperfusion injury leading to free radical formation and lipid peroxidation. This study, therefore, also investigated the possibility that cocaine-induced cytosolic enzyme release may be mediated via the formation of free radicals leading to lipid peroxidation. To test this hypothesis, muscle total glutathione levels, a free radical scavenger, and muscle thiobarbituric acid reactive substances (TBARS), a measurement of lipid peroxidation, were examined following an acute IV cocaine dose in mice. Sedentary BalbC mice were injected with cocaine (40 mg/kg) or normal saline via the tail vein. Creatine kinase levels in serum and total glutathione and TBARS in liver and muscle were determined at 4, 8, and 24 hrs. Serum creatine kinase levels were significantly elevated 5-fold, while TBARS were elevated 100% in the gastrocnemius muscle of cocaine-treated animals at 4 hrs compared to normal saline controls. However, serum creatine kinase levels, total glutathione and TBARS in the gastrocnemius muscle were not statistically different at 8 or 12 hrs; or in the liver and anterior tibialis muscle at 4, 8, or 24 hrs. The present findings suggests that lipid peroxidation may be occurring in skeletal muscle after a single IV cocaine dose in mice.