The rĂ´le of the gonadal-stimulating hormone of the anterior pituitary in the development and regulation of the genital system has been previously reported., That the same stimulation of the ovarian follicle can be effected in ovaries which have been grafted into both normal and castrated males is here reported. A series of 4 male rats, 96 days of age, may be taken as a typical group. Two of these were castrated and the ovaries of 20-day-old rats were transplanted into the recti abdomines and anchored with silk sutures. Into the other 2 unoperated males, ovaries of 20-day-old rats were transplanted, one ovary into each testis. Eight daily transplants of the fresh pituitary of an adult rat were then given to one of the castrated and one of the normal hosts. The other pair received no transplants. The rats were autopsied on the ninth day of the experiment and the grafts removed and sectioned. The ovarian grafts in the recti muscles of the castrated animals were well vascularized, but considerable degeneration, evidently due to an inadequate circulation, had occurred in the untreated animal. In the graft of the animal which had received the pituitary transplants many primary follicles had disappeared, but a score of large follicles, of mature condition and with apparently normal ova, were found. In the untreated animal of the second pair of this series, the transplanted ovary had been resorbed. In the treated animal there was a typical bilateral ovariotestis. The vascularization was unusually good, and the follicles, both primary and secondary, were numerous. Many large, apparently normal follicles in the graft were like those in a normal adult ovary, with little atresia of the follicles or ova.