Immunological, hematological, and biochemical studies were done at the time of referral in 135 homosexual subjects, 28 of whom were symptom free (SF), 74 of whom had the acquired immune deficiency syndrome (AIDS)-related symptom complex (ARC), and 33 of whom had AIDS with Kaposi's sarcoma, opportunistic infection, or both. Of 38 laboratory parameters, 11 were significantly different than controls in the SF patients, 19 in the ARC patients, and 20 in the AIDS patients. In SF patients, delayed hypersensitivity was significantly suppressed for 6 of 12 recall antigens. In addition, the percentage of circulating lymphocytes, the percentage of T3+ cells, the percentage and absolute number of T4+ cells, the T4/T8 ratio, the blastogenic responses to phytohemagglutinin, pokeweed mitogen, and concanavalin A were depressed significantly in this group. In contrast, the percentage and absolute granulocyte count, the serum lysozyme, and the serum thymosin alpha 1 were significantly elevated in these patients. In patients with more advanced disease (ARC and AIDS), immunological and hematological parameters tended to worsen. Thus, in the AIDS patients the white blood cell count, percentage, and absolute T11+ cells, absolute T3+ cells, percentage of T4+ cells and absolute level of B-cells, as well as the monocyte adherence and delayed hypersensitivity responses to 12 of 12 recall antigens were depressed. Serum levels of thymosin alpha 1 were equally elevated in all three groups. Serum interferon was found in 15 of 18 opportunistic infection patients with or without Kaposi's sarcoma, in 3 of 9 Kaposi's sarcoma patients without opportunistic infection, but in none of the ARC or SF patients. This study has demonstrated that SF sexually active homosexuals have a characteristic pattern of immune deficiency and that immunodeficiency worsens as one compares SF to ARC to AIDS patients. The study has provided a data base for the development of prognostic criteria and for characterization and evaluation of immunorestorative and immunomodulatory therapy.