In 3 series of rats, (1) normal, (2) hypophysectomized, and (3) those hypophysectomized and treated with male sex hormone prepared from urine, the weights and histologic appearance of the thyroid, suprarenal and thymus glands in the hypophysectomized animals showed alterations from the normal, but there was no appreciable difference between these organs in the treated and untreated hypophysectomized rats. In the untreated hypophysectomized animals, after 20 days, the weights of the testes, epididymis, prostate and seminal vesicles decreased and microscopic examination showed considerable atrophy; but when the hypophysectomized animals received injections of male sex hormone over a similar period, the weights of the sex glands including the testes, were maintained; and histologically the glands could not be distinguished from the normal.