Prostasomes are submicron secretory granules synthesized, stored and secreted by the epithelial cells of the human prostate gland. They are membrane-surrounded also in their extracellular appearance and the membrane architecture is composite. They are believed to be life-giving and act as protectors of the spermatozoa in the lower and upper female genital tract on their way to the ovum. Hence, the prostasomes are immunosuppressive and inhibitory of complement activation. Further, they promote sperm's forward motility and have antioxidant and antibacterial capacities. The prostasomes with their many composite abilities seem to turn against the host cell after the age of 50 y being conducive to the transition of the normal prostate epithelial cell into a neoplastic cell and therewith lay the foundations of the very high prevalence of prostate cancer of men of more than 50 y of age.