The successful use of granulocyte transfusions in a patient undergoing volunteer unrelated donor BMT for very severe aplastic anemia complicated by presumed fungal infection is described. Granulocytes were obtained by leukapheresis of normal volunteer donors stimulated by granulocyte colony-stimulating factor. The yields of granulocytes obtained by this method were sufficient to produce sustained neutrophil increments in the recipient throughout the transplant course. In vitro studies indicated that granulocytes were functionally normal, a finding which was supported clinically by the rapid resolution of infection, even in the setting of immunosuppression post-transplantation. This demonstrated the potential value of granulocyte transfusions in high-risk BMT.