Prostasomes are membrane-bound secretory vesicles produced by prostatic epithelial cells. They are known to carry many proteins, including tissue factor, and have membranes unusually rich in cholesterol and sphingomyelin. Prostasomes have well-documented effects on fertility, promoting sperm motility, stabilizing the acrosome reaction, and facilitating immunosuppression. This article reviews the evidence of the effects of prostasomes on in vitro angiogenesis assays, and the mechanism by which these effects occur. Seminal prostasomes seem to inhibit angiogenesis, whereas the equivalent particles released by malignant prostate cells promote angiogenesis. In both cases, the effects seem preserved after heat treatment to denature the protein content, suggesting an important role for lipid transfer, in particular, transfer of sphingomyelin.