Prophylactic granulocyte transfusions prevent infections in granulocytopenic marrow transplant recipients. In this setting the selection of a single "compatible" related donor for each recipient removes many of the immunologic problems inherent in utilizing multiple random volunteer donors. Graft-versus-host disease is a real risk from granulocyte transfusions and can probably be prevented by irradiation prior to infusion. The problem of cytomegalovirus acquisition through granulocyte and other blood product donors remains to be solved.