Acrosin is a serine protease located within mammalianacrosome as inactive proacrosin. Sulphated polymers bind to proacrosin and acrosin, to a domaindifferent from the active site. Upon binding, these polymers induce proacrosin activation and some ofthem, such as fucoidan, inhibit sperm binding to the zona pellucida. In this work we have studied theinteraction of solubilised zona pellucida glycoproteins (ZPGs), heparin and ARIS (Acrosome ReactionInducing Substance of Starfish) with boar and human acrosin. We have found that ARIS, solubilised ZPGsand fucoidan, but not heparin, inhibit the binding of the monoclonal antibody against human acrosinC5F10 to boar or human proacrosin. These results suggest that fucoidan, solubilised ZPGs and ARIS bindto a related domain on the proacrosin surface. Moreover, ARIS was able to induce human proacrosinactivation. On the other hand, neither ARIS nor heparin from porcine intestinal mucosa or bovine lunginduced hamster sperm acrosome reaction or sperm motility. Recent data showed that acrosin is involvedin dispersal of the acrosomal matrix after acrosome reaction. Thus, the control of the ZPG glycanchains over proacrosin activation may regulate both sperm penetration rate and limited proteolysis ofzona pellucida proteins.