Small doses of prednisolone administered on days 5-9 of gestation maintained pregnancy in protein-deficient rats. Similar results were obtained by administration of ACTH. Except for slightly smaller fetuses, the reproductive performance of animals treated with prednisolone equaled that of animals receiving ovarian hormones or transitory supplements of protein in the diet. It is suggested that maintenance of gestation by adrenocortical steroid treatment results from mobilization of maternal tissue protein.