The levels of prolactin, FSH, LH, oestradiol and progesterone were measured daily during fourteen ovulatory cycles. The behaviour of FSH, LH, oestradiol and progesterone was classical. Non-systematic changes occurred in prolactin levels during the course of the menstrual cycle with the highest level being either during the ovulatory period or during the luteal phase. However, the mean level of prolactin was significantly higher during the ovulatory and luteal phases than during the follicular phase. A direct relationship between oestradiol and prolactin levels was noted, although there was no correlation between prolactin on the one hand and FSH, LH and progesterone on the other.