SUMMARYSerial plasma levels of prolactin, follicle‐stimulating hormone (FSH), luteinizing hormone (LH), 17β‐oestradiol (E) and progesterone (P) were determined by radioimmunoassay in ten healthy women during late pregnancy and the puerperium during inhibition of lactation by Bromergocryptine. This medication was continued until the occurrence of the first menstruation, at which point an endometrial biopsy was taken. Prolactin was very effectively suppressed by Bromergocryptine in all patients, as was lactation. FSH was nearly undetectable during late pregnancy and the first week post‐partum with an increase back to normal levels between day 7 and day 12. Thereafter FSH levels were within the normal cyclic range. Following clearance of human chorionic gonadotrophin (HCG) during the first 2 weeks post‐partum, LH was found within the normal cyclic range in all patients. From day 7 E increased in nine of ten patients to reach levels during the fourth week which are seen normally at the moment of the pre‐ovulatory E‐surge in cycling women. In eight of the ten cases this was concomitant with high levels of LH. The tenth patient showed a high E level at day 36. P was fully excreted within 7 days and remained low until approximately day 20. Thereafter an increase was demonstrated with levels as found during the luteal stage of the menstrual cycle in nine patients within 33 days and within 40 days in all ten patients. The endometrial biopsies showed clear signs of secretory activity. The probable action of prolactin on ovarian function is discussed. It is suggested that during the puerperium the ovaries are the more refractory part of the hypothalamic‐pituitary‐ovarian axis, due probably to an influence of prolactin on the ovarian s