There have been many contradictory reports of the effects of androgens on the testes. In the rat the most frequently noted effect has been an adverse one (see review by Moore [1939]), and in the pigeon, too, atrophy of the testes has been produced by testosterone injections [Chu, 1940]. This adverse effect is presumably due to an inhibition of gonadotrophin production or secretion. On the other hand, the testis may be stimulated in immature or adult, intact or hypophysectomized, ground squirrels [Wells & Moore, 1936; Wells & Gomez, 1937] or in immature rats [Shay, Gershon-Cohen, Paschkis & Fels, 1941] by androgen injections. In hypophysectomized animals spermatogenic activity may be maintained by injections of androgen [Cutuly & Cutuly, 1940; Chu, 1940; and earlier reports by others] or when the testes have atrophied spermatogenesis may be partially restored in the same manner [Selye & Friedman, 1941]. The present report describes similar results