It is known that dogs and bitches exhibit a peculiar body posture during micturition. In the infantile male, the hind limbs are spread with slight drooping of the pelvis; in the adult one of the hind legs is lifted, with flexion and adduction of the limb, urine being emmitted, in most cases, against a vertical object. This adult pattern has been initiated in our dogs between 5 and 8 months of age. In the infantile or adult female there is a flexion of both hind limbs, with pronounced drooping of the pelvis. Castration and hormonal treatment of males - Castration of males over four months old does not prevent, in most animals the appearance of the adult pattern of micturition. However, in 12 males castrated when 24-61 days old, 9 maintained the infantile urinary behavior through adult age, 1 exhibited the masculine, while 2 a mixed type, (infantile and adult). It is interesting to note that even the early castrates, though urinating like infantile, displayed mating attempts, with mounting and rythmic pelvic movements. After treatment of 4 early castrates with testosterone propionate, either oily injections or subcutaneous implants, the masculine urinary behavior has been induced in 3, and a mixed in 1. 4 castrated treated with injections of estradiol benzoate have not displayed the feminine pattern of micturition. castration and treatment of females - In the bitch, as we have said, the postural pattern is the same, either in the infantile or in the adult animal. In 9 castrated between 30 and 64 days after birth, no changes have been observed, until 16 months of age. After administration of testosterone propionate to 4 normal and 5 spayed bitches, 1 has exhibited questionable effects, while in 8 no masculinization of the urinary behavior has been induced, notwithstanding the morphologic effects, with considerable hypertrophy of the clitoris. Experiments are still in course, to test the effect of a more intensive and earlier treatment with estrongens and androgens, in both sexes, beginning in the first days of life. It is concluded that in the dog the body posture during micturition is a secondary sex character and, at least in the male, controled by the gonadal hormone. Early castration prevents the appearence of the adult masculine pattern, which is exhibited after testosterone treatment. The hormonal and nervous factors involved are discussed in the paper.