This paper reports both the electrochemical characterization and the reactivity of the nitroso radical anion from nitrosobenzene with glutathione. The reduction of nitrosobenzene to the corresponding nitroso radical anion was kinetically characterized in acetonitrile. Free radicals exhibited a natural decay of second order, with a constant value of k(2) = 15 555 +/- 321 M-1 s(-1). Also, the radicals were characterized by UV-Visible and EPR spectroscopy. Data obtained with these two independent techniques clearly substantiated the formation of the nitrosobenzene radical under our experimental conditions. Furthermore, we have unambiguously demonstrated that glutathione (GSH) scavenged the nitroso radical anion electrochemically generated from nitrosobenzene. The scavenging effect of GSH is supported by the following experimental facts: 1. The parallel decrease of the anodic peak current in the cyclic voltammograms, corresponding to the nitroso radical anion concomitantly with the addition of GSH. 2. The significant decrease of the visible band at 560 nm corresponds to the radical after the addition of GSH. 3. The drop of the EPR signal intensity of the nitroso radical after the addition of GSH. By using a spin trapping technique, thiyl radical(GS) was detected during the reaction between the nitroso radical anion with GSH.