We have recently reported that older patients with HIV are deficient in glutathione (GSH) due to decreased availability of cysteine and glycine, and that oral supplementation with cysteine (as n-acetylcysteine) and glycine for 2-weeks corrects their own levels, and improves (but does not fully normalize) concentrations of red-cell GSH. We also found that when GSH deficient, subjects had impaired mitochondrial fuel oxidation and this improved with an increase in intracellular GSH concentrations. These older HIV patients also had significant increases in muscle strength with improvement of GSH levels.The current proposal in older HIV patients will investigate study if cysteine and glycine supplementation for a duration of 12 weeks will result in changes in : (a) GSH levels; (b) body composition/anthropometry; (c) strength and function; (d) quality of life; (e) mitochondrial energetics; (f) biochemistry (including dyslipidemia and oxidative stress); (g) protein and glucose metabolism; (h) cognition and memory. After completing supplementation for 3 months, GSH concentrations, strength, function, mitochondrial energetics and neurocognitive tests will be measured for a further 2 months to determine the effects of washout.