To evaluate further the immunodeficiency of homosexual men, blood and lymph node specimens were obtained from five homosexual men with lymphadenopathy and from seven homosexual men with Kaposi's sarcoma. Monoclonal antibodies were used to identify T-lymphocyte subsets in blood by cytofluorometry and in frozen sections of nodes by immunoperoxidase techniques. The homosexuals with Kaposi's sarcoma had a T-helper/suppressor ratio in blood of 0.7; the homosexuals with lymphadenopathy had a ratio of 0.6, compared with controls of 2.1. Control lymphoid tissue had a ratio of 3.0 in the interfollicular areas compared with the reactive lymph nodes in the homosexuals with lymphadenopathy, which was 0.7, and nodes from patients with Kaposi's sarcoma, 0.9. The nodes from homosexual men had evident numerous suppressor cells in the follicular center and mantle regions, locations in normal lymphoid tissue where suppressor cells were uncommon.