Dogs of 5 or more yrs. of age having varying degrees of hypertrophy of the prostate gland were used. One testis in its normal situation is sufficient to insure normal development and sustenance of the prostate gland. In the 1st group, 1 testis and its attached spermatic cord were surgically placed in the abdomen and the other testis was removed for study at the time of operation. In a 2d group, one testicle was placed in the abdomen and the other testis was allowed to remain in the scrotum. In a 3d group, 1 testis was removed and the other kept in normal position. In the 4th group, both testes were removed. Rapid progressive atrophy of the prostate gland was noted in all of the dogs of the bilateral castrate group. The dogs having a single testis which was placed in the abdomen were examined 270-798 days after operation; the prostatic gland showed hypertrophy, whereas the testis showed atrophy. Dogs having one testis in its normal position in the scrotum, the other testis having been placed in the abdomen or removed, were examined 230-1589 days after operation; no evidence of atrophy of the prostate was found. Thus, the surgically produced cryptorchid testis retained its ability to sustain the prostate gland. The failure of development of the prostate gland in dogs with congenital crytorchidism is probably due to the associated failure of testicular development.