Murine monoclonal antibodies (MoAbs) were isolated to characterize antigenically distinct subpopulations of human sperm. Spleen cells from Balb/c mice immunized with freshly prepared human sperm, were fused with murine P3-NS1-Ag4-1 myeloma cells by somatic cell hybridization, and supernatants from the IgG-secreting hybridomas were screened by an enzyme immunoassay (EIA) for reactivity against fresh human sperm and a panel of human somatic cells. Two MoAbs, SP1D1 and SP7A7, reacted specifically with human sperm, whereas three others, SP2A9, SP3B3, and SP4F5, cross-reacted with a variety of human somatic cells. The binding of MoAbs were characterized by immunofluorescence, agglutination, and Staphylococcus aureus binding assays. We found that certain MoAbs bound to common antigens of the head and tail, or to tail alone, and had agglutinating activity. However, not all sperm were reactive to antibody, and the binding activity could only be demonstrated in subpopulations of sperm ranging from 5 to 50% of the total number.