Our recent work has shown for the first time the translation of nuclear-encoded proteins in mammalian spermatozoa. We demonstrate that several sperm proteins are degraded after a relatively long period of incubation, and some of these proteins are resynthesised when sperm were incubated under capacitation conditions. In the present study using specific antisenses we demonstrated a significant reduction in the level of several sperm proteins and inhibition of sperm motility, actin polymerization and the acrosome reaction. Thus, this study further supports our previous notion regarding the synthesis of proteins during sperm capacitation.