A 10-year-old girl was first seen at age 5 years with pneumonia and neutropenia. Since then, she has remained leukopenic, although manifesting a leukocytosis only when she has pulmonary infection. A rapid fall in her peripheral WBC count occurs with initiation of antibiotic therapy. Despite her neutropenia, marked myeloid hyperplasia is evident on marrow smear examination; many cells being hypersegmented with fine intralobular bridging with chromatin strands and cytoplasmic vacuolation. The peripheral WBC response to epinephrine adminstration did not indicate a shift from the circulating to marginal neutrophil pool. Results from a Rebuck skin window test suggested poor neutrophil tissue migration. A defect in granulocyte release from the patient's marrow may explain these bizarre hematologic findings.