Seminal PGE, 19-OH PGE and fructose were assayed in normal volunteers and in infertile patients. From data obtained it appears that seminal PGE are probably not synthesized exclusively at seminal vesicles level since no relationship was observed between PGE and fructose. On the other hand the seminal vesicles appear to be the preferential site of seminal 19-OH PGE production since a close relationship was observed between 19-OH PGE and fructose in those case in which these prostaglandins were below minimum normal values. Various hypotheses are advanced in order to interpret the lack of correlation in the presence of high 19-OH PGE levels.