Body cells and tissues are threatened continuously by damage caused by toxic free radicals and reactive oxygen species (e.g., peroxides) which are produced during normal oxygen metabolism, by other chemical reactions, and by toxic agents in the environment. Free radicals are capable of disrupting metabolic activity and cell structure. When this occurs, additional free radicals are produced which, in turn, can result in more extensive damage to cells and tissues. The uncontrolled production of free radicals is thought to be a major contributing factor to many degenerative diseases. Glutathione is a naturally-occurring tripeptide of L-cysteine, L-glutamate and L-glycine. Glutathione is the essential co-substrate for two major antioxidant enzymes in the body; glutathione peroxidase and glutathione reductase. As such, glutathione offers one mechanism for scavenging toxic free radicals. Glutathione is well absorbed in the intestine, and enters the blood and other extracellular compartments where it exerts much of its beneficial antioxidant effects. N-Acetyl-L-Cysteine is efficiently transported into the cell where it is readily converted to cysteine for glutathione synthesis. Thus, supplementation with N-Acetyl-L-Cysteine can help raise intracellular glutathione levels. N-Acetyl-L-Cysteine also appears to have antioxidant properties as such, and is a valuable sulfur donor for various metabolic needs.