Reduced glutathione (GSH) is one of the most preferred biological substrates of myeloperoxidase-derived hypochlorous acid and is a likely target for neutrophil oxidants. We have used HPLC to show that the oxidation of GSH by hypochlorous acid gives two major, stable products in addition to glutathione disulphide (GSSG). The most prevalent product lacks free amine and thiol groups, and was shown by electrospray MS to have a molecular mass of 337 Da. This corresponds to GSH with a gain of two oxygen atoms and a loss of two hydrogen atoms, and is consistent with the product being an internal sulphonamide. The other novel product has a molecular mass of 644 Da, and has amine groups but no free thiols. These properties are consistent with it being glutathione thiolsulphonate. Whereas GSSG in the cell is recycled enzymically, formation of these higher oxidation products is likely to be irreversible. Hypochlorous acid, therefore, could compromise the cell by depleting GSH. The putative sulphonamide may be unique for oxidation by hypochlorous acid and thus provide a useful marker of neutrophil oxidant activity.