Several separate events of the fertilization sequence (sperm capacitat
ion, regulated sperm transport in the oviduct, sperm-cumulus interacti
on, sperm-zona binding, the acrosome reaction, zona penetration, gamet
e fusion) represent points at which conception might be preventable. E
ach is considered variously with reference to its biological significa
nce, what is known about the mechanisms involved, the issues that rema
in to be resolved, and the prospects for specific inhibition.