Continuous and prolonged administration of corticotrophin (ACTH) to single foetal lambs at gestational ages of 88–129 days was followed by parturition on the 4th–7th day of the infusion. At birth, the foetal adrenal glands weighed at least as much as those of normal lambs at term. Infusions of cortisol into the foetus at a rate of 50 mg./24 hr. was followed by premature parturition within 5 days. Prolonged administration of the same doses of ACTH or cortisol to pregnant ewes and of oestradiol-17β to a foetus did not cause parturition. These observations indicate that the pituitary-adrenal system of the foetus may play an active part in the initiation of parturition in the ewe.