The effect of vitamin E deficiency on the levels of lipid peroxide and solubility of collagen was investigated in Wistar rats that were fed a vitamin E deficient diet for 3 and 6 months. The lipid peroxide content in the skin and subcutaneous tissue was markedly increased as compared with that of control rats on a normal diet. The lipid peroxide content in the tissues of rats deficient in vitamin E for 3 months, was greater than that found in those on the diet for 6 months. The effect of UV irradiation on the lipid peroxide content in the skin of control rats was not significant, but there was a marked difference in lipid peroxide content in those animals on a deficient diet. The amount of insoluble collagen in the skin of rats on a vitamin E deficient diet for 6 months was increased and by more than in those animals on the diet for 3 months. The amount of soluble collagen in the rats deficient in vitamin E for 6 months was markedly reduced when compared with those on the diet for 3 months. These results suggest that vitamin E deficiency promotes the peroxidation of lipids and accelerates the cross-linking of collagen in the skin.