Effects of sperm-immobilizing antibodies on sperm-zona pellucida tight binding**This work was partially supported by the Contraceptive Research and Development Program (CONRAD), Eastern Virginia Medical School, Norfolk, Virginia, under a Cooperative Agreement (DPE-2044-A-00-6063-00) with the United States Agency for International Development (A.I.D.) and Research Grant from Hyogo Medical College, Nishinomiya, Hyogo, Japan. The views expressed by the authors do not necessarily reflect the views of A.I.D.