The present experiment was designed to investigate the effect of selenium (Se) supplementation, as sodium selenite, on organic solvent-soluble lipofuscin pigment (OLP) accumulation and glutathione peroxidase (GSH-Px) activity in the livers of mice fed varying levels of vitamin E or N,N'-diphenyl-p-phenylenediamine (DPPD). Four groups of 16 female, weanling mice each were fed either a vitamin E-deficient diet, a diet supplemented with 30 mg/kg or 300 mg/kg vitamin E (as RRR-alpha-tocopheryl acetate), or a diet supplemented with 30 mg/kg DPPD. Each diet contained 0.05 ppm Se. At 5 months of age, eight animals from each dietary group were supplemented with an additional 0.1 ppm Se, as sodium selenite, in their drinking water. The remaining animals were fed their original diets through the 9-month experimental period. Selenite supplementation resulted in a significant increase in OLP concentration and GSH-Px activity in the liver of mice fed vitamin E- or DPPD-supplemented diets. Normal levels of vitamin E and DPPD (30 mg/kg) were not sufficient to protect against the oxidative effects of selenite; however, 10 times the normal level of vitamin E (300 mg/kg) markedly suppressed this oxidative effect.