Peripheral blood mononuclear cell populations in ten men, with idiopathic infertility with serum sperm agglutinating antibodies at a titre of 1/32, were evaluated. Mononuclear cells were enumerated using the monoclonal antibodies OKT3 (pan T cells), OKT4 (helper/inducer T cells), OKT8 (suppressor/cytotoxic T cells), Leu 7 (monocytes, null cells, and natural killer (NK) cells), OKIa (B cells, monocytes, null cells and activated T cells). Blood mononuclear cells with surface receptors for complement (B lymphocytes and a proportion of monocytes and null cells) were enumerated using a rosette test (EAC). The following abnormalities, compared to normal subjects, of blood mononuclear cell population were found: a decreased percentage of OKT3 (+) cells (p less than 0.01), a decreased percentage of OKT8 + cells (p less than 0.001) and increased OKT4/OKT8 ratio (p less than 0.001), an increased percentage of OKIAI cells (p less than 0.001). Levels of OKT4+ and Leu 7 cells and the percentage of EAC rosette forming cells were not significantly different from those in normal subjects. Regression analysis showed a significant correlation between the percentage of OKIAI cells and sperm agglutinating antibodies. After all that, significant correlation between humoral and cell-mediated immunity in patients with idiopathic infertility with antisperm autoantibodies, were observed.