The techniques of pulse radiolysis, laser photolysis, and absorption spectroscopy have been used to investigate the glutathione disulfide radical anion formation over the pH range 7.0-13.0 in aqueous solution. Photolysis of the disulfide anion formed from the one-electron oxidation of reduced glutathione perturbs the disulfide anion/thiyl radical equilibrium, allowing the rate constant for thiyl radical reaction with glutathione to be uniquely determined from the transient absorption bleach and subsequent pseudo-first-order recovery. These pH-dependent values were combined with measured disulfide equilibrium constants to calculate glutathione radical anion dissociation rate constants. From computer modeling of established mechanisms of the observed disulfide radical anion growths, pH-dependent rate constants for the reaction of hydroxyl radicals with glutathione to produce the thiyl radical were obtained. Utilizing literature ionization constants, values for hydroxyl and thiyl radical reactions with individual glutathione species were determined. The similarity of the measured values over the pH range 10-13 suggests that the rate constants for both the hydroxyl and oxide radical reaction with glutathione are essentially the same. These hydroxyl radical rate constants are contrasted with previously reported values determined using competition kinetics.