A particularly important family of antioxidant defence enzymes in the body are the glutathione peroxidases, which remove H(2)O(2) by coupling its reduction to H(2)O with oxidation of reduced glutathione (GSH) to oxidised glutathione (GSSG). There are suggestions that GSH in the peripheral blood may be reduced in myalgic encephalomyelitis, which is a highly disabling neurological disease of unknown aetiology. Since many of the symptoms relate to cerebral functioning, it would seem probable that peripheral blood GSH findings would be reflected in lower cerebral GSH levels. The aim of this study was to carry out the first direct assessment of cerebral GSH levels in myalgic encephalomyelitis; the hypothesis being tested was that cerebral GSH levels would be reduced in myalgic encephalomyelitis. Cerebral proton neurospectroscopy was carried out at a magnetic field strength of 3T in 26 subjects; spectra were obtained from 20x20x20mm(3) voxels using a point-resolved spectroscopy pulse sequence. The mean cerebral GSH level in the myalgic encephalomyelitis patients was 2.703 (SD 2.311) which did not differ significantly from that in age- and gender-matched normal controls who did not have any history of neurological or other major medical disorder (5.191, SD 8.984; NS). Therefore our study does not suggest that GSH is reduced in the brain in myalgic encephalomyelitis. At the present time, based on the results of this study, there is no evidence to support the suggestion that, by taking glutathione supplements, an improvement in the brain-related symptomatology of myalgic encephalomyelitis may occur.