Ten groups, five to ten animals per group were used in demonstrating that progesterone plus cortisol acetate can induce implantation and maintain embryonic growth in hamsters subjected to ovariectomy and adrenalectomy on Day 1 or on Day 4 of pregnancy. Fetal weights on Day 14 were, however, significantly lower than in sham-operated control animals, although they were not different from those in animals only ovariectomized and given progesterone. It is concluded, therefore, that it is unnecessary to invoke secretion of estrogen either from the ovaries or from the adrenals for induction of implantation in hamsters.