Up to the present time, the most extensive knowledge in prostaglandin research has been achieved in the field of reproductive physiology. It seems now certain that prostaglandins are involved in each phase of the reproductive process although their precise physiological functions cannot yet be completely explained. For example they are thought to play an important role in the hypothalamic -- pituitary system in the liberation of LHRH and in the ovary in steroid genesis, ovulation and luteolysis; also, in the non-pregnant uterus in the onset of menstruation while at conception both sperm and ovum transport are influenced by prostaglandins. In pregnancy, a prostaglandin function has been demonstrated in the uterus in initiating labour in cases of abortion and in birth at term. Further, they appear to be involved in regulating the blood circulation in placenta, cord and fetus. Already, because of their established physiological functions, the prostaglandins have been introduced successfully into clinical use.