We describe a very rapid high-performance capillary electrophoresis method for the separation and quantification of reduced (GSH) and oxidized (GSSG) glutathione in red blood cells. Two procedures for sample preparation have been compared, Microcon-10 membrane filtration and acid precipitation. The separation is obtained in an uncoated capillary using a high ionic strength borate buffer at pH 7.8. The intra-assay coefficients of variation (CVs%) are 1.53 and 1.66 for GSH and GSSG, respectively. The run is shorter than 90 s and the migration time is highly reproducible both for GSH (CV% 0.22) and GSSG (CV% 0.17). When the filtration step is used only GSH is found, whereas both GSH and GSSG are detectable after acid precipitation, suggesting that GSSG revealed after acid treatment may be an artefact due to GSH oxidation. Because of its good analytical performance this method could be used for routine red blood cell glutathione measurement in healthy or pathological conditions.