Electron spin resonance (ESR) and spin trap methodology were used to investigate the reduction of chromate (13907454) by glutathione (GSH) and find evidence for the involvement of the glutathionyl (GS) radical as well as chromate-V (Cr(V)) intermediates. While an aqueous solution of 0.1 molar spin trap alpha-(4-pyridyl-1-oxide)-N- tert-butylnitrone (4-POBN) containing either chromate or GSH alone did not give any ESR signal, mixtures of chromate, GSH, and 4-POBN together gave a spectrum which was a composite of the spin adduct signal and those of Cr(V). About 10 minutes later, when the signal from Cr(V) had decayed, a clear spectrum (at g of 2.0061) consisting of only doublets of triplets was obtained and was assigned to the 4- POBN-GS adduct. The GS radical had been produced via reaction of GSH with alpha-chromanoxyl radical. Spin trap studies with 5,5- dimethyl-1-pyrroline-1-oxide (DMPO) provided additional support for the identification. The spin trap studies indicated that an increase in the amount of GSH caused an increase in the spin adduct ESR signals until the intensity leveled off at a molar ratio of about 15 to 1 of GSH to potassium-chromate (7789006). The authors conclude that the results of the GS radical and Cr(V) at high GSH levels suggests that the synergistic reaction of the Cr(V) intermediate and the GS radical are perhaps responsible for the increased chromate-IV induced DNA strand breaks at high GSH levels.