Studied was the content of vitamins A and E as well as that of fats, aldehydes, and peroxides and the biologic activity of vitamin E with regard to the amount of santoquin in combined forage mixtures for birds. The experiments were carried out with a finisher forage mixture for broilers to which santoquin was added in amounts of 0.010, 0.016, 0.020, and 0.025 per cent. It was found that at an antioxidant concentration of 0.020 per cent a best protection of the biologic vitamin E activity was provided. The rapid inactivation of vitamin E at a level of santoquin lower than 0.016 per cent was associated with the intense deposition of products of the final oxidation when fats turned rancid. Taking into consideration the importance of fats as a source of energy a 0.020 per cent level of santoquin in the forage mixtures for broilers is suggested.