United States Biological has improved the standard GSH/GSSG Assay Kit by using a new and improved GSH scavenger. Reduced glutathione (GSH) is a tripeptide (gamma-glutamylcysteinylglycine) that contains a free thiol group. GSH is a major tissue antioxidant that provides reducing equivalents for the glutathione peroxidase (GPx) catalyzed reduction of lipid hydroperoxides to their corresponding alcohols and hydrogen peroxide to water: H2O2 + 2GSH ---------> GSSG + 2H2O (catalyzed by GPx) In the GPx catalyzed reaction, the formation of a disulfide bond between two GSH molecules gives rise to oxidized glutathione (GSSG). The enzyme glutathione reductase (GR) recycles GSSG to GSH with the simultaneous oxidation of beta-nicotinamide adenine dinucleotide phosphate (beta-NADPH): GSSG + NADPH -----------> 2GSH + NADP+ (catalyzed by GR) When cells are exposed to increased levels of oxidative stress, GSSG will accumulate and the ratio of GSH to GSSG will decrease. Therefore, the determination of t