During the past two decades a number of agents and dietary regimens have been reported to be teratogenic when administered to pregnant mammals. The diversity of the teratogenic agents and the similarity of the congenital defects induced have led to considerable speculation regarding the mechanisms involved. Since most procedures subjected the maternal organism to a certain degree of stress, it was suggested by Seyle ('SO,'51) and Fraser et al.('51a,'54) that the products of hyperactive maternal adrenal cortices might be the primary causal factor in many of the forms of induced congenital anomalies. The reports of Fraser and associates (% la,'5lb, 53a,'53b,'54), and Kalter and Fraser ('52,'53) on the production of cleft palate in the offspring of mice treated with cortisone, hydrocortisone or adrenocorticotropin have provided considerable support for this general concept. In addition, Fainstat ('54) recently reported the appearance of cleft palate in the offspring of rabbits treated with cortisone. In view of the important implications in the reports of Fraser and his associates the following investigation was undertaken in order to ascertain whether the normal course of pregnancy in the rat could also be altered by the administration of an exogenous adrenal steroid.