The effect of hypophysectomy on pseudopregnancy in the rabbit has been studied. When the hypophysis is removed during pseudopregnancy, the corpora lutea atrophy and the endometrium ceases to be progestational. When ovine prolactin is given following hypophysectomy milk secretion is produced, but the corpora lutea and endometrium atrophy to the same degree as with hypophysectomy alone. Ovine luteinizing hormone given after hypophysectomy allows a considerable degree of maintenance of the corpora lutea, and the endometrium remains progestational. (Endocrinology74: 453, 1964)