Complexes of arsenic compounds and glutathione are believed to play an essential part in the metabolism and transport of inorganic arsenic and its methylated species. Up to now, the evidence of their presence is mostly indirect. We studied the stability and chromatographic behaviour of glutathione complexes with trivalent arsenic: i.e. As-III(GS)(3), MA(III) (GS)(2) and DMA(III)(GS) under different conditions. Standard ion chromatography using PRP X-100 and carbonate or formic acid buffer disintegrated the complexes, while all three complexes are stable and separable by reversed phase chromatography (0.1% formic acid/acetonitrile gradient). As-III(GS)(3) and MA(III)(GS)(2) were more stable than DMA(III)(GS), which even under optimal conditions tended to degrade on the column at 25 degreesC. Chromatography at 6 degreesC can retain the integrity of the samples. These results shed more light on the interpretation of a vast number of previously published arsenic speciation studies, which have used chromatographic separation techniques with the assumption that the integrity of the arsenic species is guaranteed.