Human sperm fertilizing potential in vitro is correlated with differential expression of a head-specific mannose-ligand receptor**Supported in part by grant RR05924 from the National Center for Research Resources Biomedical Research Support Program, National Institutes of Health, Bethesda, Maryland.††Presented in part at the 39th Annual Meeting of the Society for Gynecologic Investigation, San Antonio, Texas, March 18 to 21, 1992.