Allogeneic bone marrow recipients exhibit a complex and multifactorial immunodeficiency affecting numerous effector functions for various periods of time. In order to evaluate their Fc-mediated monocyte-macrophage (MM) function we studied the clearance of IgG-coated Rh-positive erythrocytes (EA) in healthy control subjects and recipients of unmanipulated marrow. We measured the survival of radiolabeled EA prior to myeloablation and on days 0, +14, +38, +124, +368, and greater than or equal to +730 following bone marrow transplant (BMT). Simultaneously we evaluated the interaction of adherent peripheral blood monocytes (PBMs) with EA (in vitro phagocytosis and attachment). Fc-mediated function appeared normal prior to BMT despite the fact that most patients had received chemotherapy previously. We found no deficit in the Fc-dependent MM activity (in vivo and in vitro) at any time after transplantation. On the contrary we demonstrated an enhanced Fc-dependent clearance during the first month after BMT (p less than 0.001; Mann-Whitney test). These results suggest that we can expect efficient MM function to eliminate IgG-coated cells and particles in BMT recipients.