induction of the human sperm acrosome reaction with mannosecontaining neoglycoprotein ligands in the interest of classifying cases of male factor infertility we have paid particular attention to the sugar ligand binding properties of the human sperm surface and the functional capacity of the acrosome for exocytosiskey parameters for assessing sperm fertilizing ability zona recognition and binding involve the interactions of sperm surface mannose receptors lectins with mannose ligands on the zona pellucida sperm surface mannose lectins can be visualized by their ability to bind a synthetic model zona ligand fluorescein isothiocyanate fitcconjugated mannosylated bovine serum albumin bsa manfitcbsa we now report that manfitcbsa biologically also mimics the effects of solubilized authentic human zonae in that binding of manfitcbsa results in a timedependent receptor aggregation and the induction of acrosome exocytosis in capacitated sperm populations from fertile donors in our assay the addition of mm amounts of mannose monosaccharide to manfitcbsa increases the number of polyvalent mannose ligands bound by individual spermatozoa and increases the rate of the acrosome reactions induced by manfitcbsa thereby increasing specimen processing efficiency we conclude that exposure of human spermatozoa to polyvalent mannose ligands dmannose monosaccharide offers a new convenient and readily available system to study sperm capacity for induced acrosome loss