AbstractBacterial sepsis is a major cause of morbidity and mortality in the neonatal period. Deficiencies in neutrophil chemotaxis, phagocytosis, and bacterial killing have all been proposed as factors possibly responsible for this problem. In addition, the neutrophil storage pool, or all segmented neutrophils, band neutrophils, and meramyelocytes/kg body weight stored within the marrow, appears to be very small in neonates compared to that in adults, and when an infection develops in a neonate, neutrophil production from stem cells may be limited. In this paper we review the evidence for these neonatal neutrophil deficiencies and examine the animal and clinical studies which have tested leukocyte transfusion as a possible adjunctive therapeutic modality for sepsis neonatorum.