Monocyte function was studied in 20 hospitalized elderly and 23 young adult subjects. 99mTc-monocyte chemotaxis, glass adhesion, S. aureus 14C-alanine phagocytosis and 51Cr-erythrocyte cytotoxicity (Natural Killer) (NK) and Antibody-mediated (ADCC) activities were studied. Monocyte function, as determined by the above test, was not significantly depressed in the elderly when compared with the young adult control group. Our results suggest that the immunologic abnormalities and the increased risk of infections observed with aging cannot be attributed to a deficit in monocyte function.