Prostaglandins were discovered almost forty years ago, but their elucidation physiologically is in its infancy today. It was only in 1957 that the first prostaglandin, PGF1-alpha, was crystallized from sheep seminal vesicles. By 1966, all of the known fourteen natural prostaglandins had been synthesized from commercially available materials. Research data has been compiled at a remarkable rate during the last three to five years.