Various aspects of monocyte-associated function were evaluated in the peripheral blood mononuclear cells of male homosexuals who were infected with the human immunodeficiency disease virus (HIV). The functional assessments included indomethacin-sensitive regulation of blastogenesis and lymphokine-activated killer (LAK)-cell induction, chemiluminescent responses of mononu-clear leukocytes to opsonized zymosan, and the expression of HLA-DR antigen on CD-14-positive monocytes. The results obtained demonstrate that each of these functions is abnormal in asymptomatic individuals who have HIV core antigen (p24) in their circulation. These results suggest that monocyte abnormalities which could contribute to immune dysfunction in HIV-infected patients can be detected early during the course of HIV infection and are associated with the expression of serum HIV antigen.