Indices of lipid peroxidation were investigated in muscle tissues of 1) calves depleted of vitamin E and/or Se and 2) calves depleted of vitamin E and Se and fed daily supplements of polyunsaturated fatty acids (PUFA). Calves deficient in both vitamin E and Se or deficient in vitamin E alone showed elevated muscle concentrations of thiobarbituric acid-reactive substances (TBARS), ascorbate-induced TBARS (ATBARS), ascorbate-induced hexanal and iron-induced 4-hydroxynonenal (HNE). Muscle tissue of calves depleted of Se alone showed no increases in these indices of lipid peroxidation. Two further groups of calves were fed diets either sufficient or deficient in both vitamin E and Se. Both of these groups were then fed linseed oil, protected against ruminal hydrogenation, as a source of PUFA. The deficient animals had higher muscle concentrations of all three indices of lipid peroxidation than the supplemented calves. Furthermore, feeding PUFA to vitamin E and Se deficient animals increased muscle concentrations of induced HNE to levels above those in deficient animals not fed PUFA supplements.