Antilymphocyte antibodies were studied using the Terasaki microcytotoxicity technique in 21 gay patients including 7 with Kaposi's sarcoma, 5 with opportunistic infection, and 9 with lymphadenopathy syndrome. A significant increase in lymphocyte-reactive antibody was noted in 61% of this group. Similar studies using serum from 25 apparently healthy gay males showed lymphocytotoxic antibody in only one instance. When isolated T-cell subsets (OKT4+ or OKT8+) were utilized, a few sera from acquired immune deficiency syndrome (AIDS) patients apparently showed preferential killing for helper-inducer or suppressor-cytotoxic T-cell subsets, however, this showed no correlation with T-cell phenotypic profiles of OKT4 or OKT8+ cells in concurrent peripheral blood studies. When isolated normal OKT4 or OKT8 T-cell subsets were treated with complement and AIDS serum showing apparent T-cell subset specificity and treated T cells added to B cells, macrophages, and OKT4 or OKT8 cells cultured with pokeweed mitogen, no discernible effect on either help or suppression of IgG or IgM synthesis was recorded.