Evolution, during growth, of basal plasma concentration of corticosterone and the adrenocortical response to psychic aggression was studied in animals of both sexes, normal or gonadectomized on the day of birth. 1. In the control animals : (a) The fluctuations of the basal plasma concentration of corticosterone took a similar course in the male and female; no significant difference was observed between males and females except on the 55th day. (b) The intensity of the response to aggression took the same course in all the test animals between the 15th and 60th day with an increase between the 15th and 45th day and a decrease between the 45th and 60th day. 2. In the animals whose gonads were removed at birth, the basal plasma concentration of corticosterone and the response to psychic aggression developed in a similar manner in the two sexes, during the period studied. 3. These results suggest the existence of an autonomous maturation of the adrenocortical function which is independent of genetic sex and gonadal secretions. These latter, however, play a determinant role in the amplitude of the response which is increased by estrogens and decreased by androgens. The existence of a mechanism whose maturation is accomplished, in part, independently of the gonadal secretions and is responsible for the response to aggression is discussed.