Concentrations of plasma vitamin E, red blood cell (RBC) vitamin E and RBC glutathione peroxidase activity in patients with sickle-cell anaemia were compared with those of age-matched normal controls. Also, the ability of vitamin E to inhibit lipid peroxidation in sickle cell RBC in vitro was measured. Plasma and RBC concentration of vitamin E were lower in 54 patients with sickle-cell anaemia (0.61 plus or minus 0.19 ml/100 ml, mean plus or minus s.d.) than in 16 controls (0.89 plus or minus 0.25). The amount of vitamin E in sickle-cell RBC available to protect lipids against peroxidative damage was significantly less (1.19 plus or minus 0.30 mu g/ml RBC, or 7.8 X 10-4 mol/mol lipid phosphorus, mean plus or minus s.d.) than that in normal RBC (1.92 plus or minus 0.34 mu g/ml RBC, or 15.0 X 10-4 mol/mol lipid phosphorus). In contrast, RBC glutathione peroxidase activity was high in sickle-cell patients (73 plus or minus 7.0 IU/g haemoglobin, mean plus or minus s.d.) compared with the normal (47 plus or minus 6.0). There was a significant negative correlation between RBC vitamin E and glutathione peroxidase activity in these patients. The increased susceptibility in vitro of sickle cell RBC to peroxidation was corrected toward normal by incubating sickle-cell RBC with vitamin E.