The effect of dietary linoleic acid and selenium on vitamin E requirement has been investigated. Groups of newly hatched, male Peking ducklings were kept for 4 weeks on diets containing increasing amounts of vitamin E (D α-tocopherol acetate). The dietary fat (35 cal%) consisted of lard (low linoleic acid content), tocopherol-free maize oil (high linoleic acid content) or natural maize oil. In addition to D α-tocopherol acetate, some groups received 0.1 mg selenium (Na2SeO3) per kg food. Vitamin E deficiency manifested itself by myopathy of all types of muscles. The skeletal muscles showed the typical hyaline degeneration. Necrocalcinosis was found in the muscular tissue of heart, gizzard and intestine. The lard diet needed 13.5 and the tocopherol-free maize oil diet 27 mg vitamin E/kg food to prevent myopathy; this is 86 and 172 mg D α-tocopherol per kg fat, respectively. For the natural maize oil, this requirement was amply covered by its own tocopherol content, while on lard diets all animals died within 3 weeks, showing severe myopathy when extra vitamin E had not been added. The increased vitamin E requirement of the animals on the tocopherol-free maize oil diet could be explained by their lower blood-tocopherol level, as compared with the lard group, at an equal dietary level of vitamin E. Selenium was found to be most effective in preventing myopathy (0.1 mg Se ≧ 20 mg D α-tocopherol acetate). The beneficial effect of selenium could not be explained by an increase of the plasma tocopherol level. Obviously, most animal fats are inadequate in vitamin E, whereas vegetable oils with a high linoleic acid content (sunflower, maize, safflower) must be considered as the natural sources of this vitamin. It is concluded, that a critical dietary E/PUFA ratio (intake of mg D •α-tocopherol, divided by the intake of polyunsaturated fatty acids in g) does not exist.