Nutritional muscular dystrophy (NMD) in the chick results from a simultaneous deficiency of vitamin E and cystine. Muscle and liver of dystrophic and nondystrophic chicks were assayed for nonprotein sulfhydryl (NP-SH), reduced glutathione (GSH) and glutathione reductase. Red blood cells were assayed for NP-SH and GSH content. Glutathione peroxidase was determined in muscle, plasma and liver. Dystrophic muscle GSH was increased and at times was approximately double that of normal muscle, while liver GSH was lower in dystrophic than in normal chicks. During recovery from NMD, brought about by addition of either vitamin E or cystine to the dystrophogenic diet, muscle GSH declined and liver GSH increased to normal levels. Glutathione peroxidase was equivalent in both dystrophic and nondystrophic plasma and liver, but was significantly increased in dystrophic muscle. The mode of action of dietary cystine in preventing NMD in chicks remains unknown; it is not mediated through the role of amino acid as a component of the GSH needed for the action of glutathione peroxidase.