ABSTRACT: Titers of hemagglutination and cytotoxic antibodies to sperm were determined in the sera, seminal plasma, cervical mucus, and vaginal secretions from 69 infertile couples, using sperm from the husbands and from normal control subjects. Titers of hemagglutination and cytotoxic antibodies were significantly higher (p = 0.002 and p < 0.001, respectively) against autologous sperm as contrasted with sperm from control subjects in sera from 55 autoimmune males. Hemagglutination and cytotoxic antibody titers were also significantly higher (p = 0.044 and p < 0.001, respectively) against their husbands' sperm as contrasted with control sperm in sera from 46 females with isoimmunity to sperm. Ninety percent of males and females with sperm immunity were positive for histocompatibility antigens HLA-B7, HLA-B8, and/or HLA-BW35. In males, the presence of increased serum cytotoxic antibody titers against autologous versus control sperm was significantly associated with the presence of HLA-B7 allele (p = 0.0017) and with HLA-B7, HLA-B8, and/or HLA-BW35 in general (p < 0.05). In the females, increased serum antibody titers to their own husbands' versus control sperm were not preferentially associated with HLA-B7, HLA-B8, or HLA-BW35 antigens.