The effect of dietary selenium and vitamin E on the important cellular antioxidant defense systems was studied in rat erythrocytes. Weanling male Sprague-Dawley rats were fed a basal selenium and vitamin E deficient diet and supplemented with either none or 0.5 ppm selenium and either none or 45 ppm vitamin E for 35 or 40 days. Depletion of dietary selenium resulted in marked decrease of glutathione (GSH) peroxidase in the red cells, but the levels of GSH, catalase and superoxide dismutase were not significantly altered. The red cells of rats fed the basal diet deficient in both selenium and vitamin E had significantly lower levels of GSH and GSH peroxidase, but not of catalase and superoxide dismutase, than in those fed the basal diet and supplemented with either selenium, vitamin E or both. The results suggest that depletion of dietary selenium and vitamin may have a precipitate effect on lowering the levels of GSH and GSH peroxidase in rat erytyrocytes.