Using the electron spin resonance method, the effect of antioxydants on the number of natural organic free radicals is studied in the case of the diaphragm of the Rat. The effect observed shows an important decrease in the free radical concentration, which may, in the case of ascorbic acid and BHT, lead to their complete disappearance. These results are discussed in the light of the hypothesis according to which antioxydants play a role in the lengthening of the life span because of their fundamental character of inhibitors of free radicals.