 GSH is the major intracellular antioxidant, the biosynthesis of which is dependent on cysteine availability.We hypothesized that supplementation with a whey-based cysteine donor [Immunocal] designed to augment intracellular GSH would enhance performance.Twenty healthy young adults (10 men, 10 women) were studied presupplementation and 3 mo postsupplementation with either Immunocal (20 g/day) or casein placebo.