Observations from 1930 to 1934 have indicated autopharmacological effects of human seminal fluid. The active principle was shown to be an unsaturated lipid‐soluble acid. After isolation in 1960 of two closely related compounds, the chemical constitution was established. From the parent compound, called prostanoic acid, a numerous family of compounds have been derived and isolated. Prostaglandins are present in high concentrations in human and sheep scminal fluid, being formed in the seminal vesicles and in the vesicular gland. They also occur in low concentrations in a great variety of tissues, including lung, nervous tissue, and menstrual fluid. The chief component in seminal fluid, prostaglandin E., lowers blood pressure, stimulates various smooth muscle organs, inhibits uterine movements, lipolysis, and gastric juice secretion, and causes sedation when administered into brain ventricles. Prostaglandins exert well‐marked synergistic and antagonistic actions with catecholamines on some organs. it has been suggested that prostaglandins are of importance for male and female sexual functions, in addition to metabolic actions, primarily on lipid metabolism, and actions on the nervous system and blood pressure.