The prostaglandins probably play an important role in the physiology of reproduction. In women as in men, they intervene at several levels. At the level of the ovary, the prostaglandins E may be modulators of the action of gonadostimulin on ovarian hormonogenesis, in close relationship with cyclic AMP and, furthermore, represent an important biochemical intermediate stage in the mechanism of ovulation. F2 prostaglandin, F2 alpha, on the other hand, represents in numerous animals, but not in women, a luteolytic factor of uterine origin. At the level of the hypothalamopituitary axis, E prostaglandins may modulate hypothalamic neuro-secretion and to a lesser degree, the liberation of pituitary stimulins, and thus intervene in gonadotropic function. At the level of the female genital tract, prostaglandins may influence uterine and tubal motility. It is perhaps by this latter effect that the very large quantities of seminal prostaglandin influence the process of fertilisation.