Cytotoxic and immunobead-binding antibody assays were used to document possible changes in antigenicity after the spermatozoa were subjected in vitro to capacitating conditions. Serum and seminal plasma immunobead-binding immunoglobulin (Ig)A, sperm surface IgG, and IgA, and seminal plasma cytotoxic antibody titers in 26 autoimmune infertile men were decreased against autologous spermatozoa under capacitating conditions. Cytotoxic antibodies and immunobead-binding IgG, IgA, and IgM against husbands' sperm undergoing capacitation, in the cervical mucus of these women, were less than those against uncapacitated sperm. Conversely, sperm antibody levels were increased against the capacitated husbands' sperm in the husbands' serum and wives' cervical mucus, originally testing negative for cytotoxic antibodies against uncapacitated sperm. Antibody levels were unaltered against donors' sperm undergoing capacitation, except for a reduction in titers in the serum of isoimmune wives. The differences in sperm antibody assay results, depending on whether or not spermatozoa are incubated under conditions favoring capacitation, are specific to the husbands' and not to the donors' spermatozoal antigens.