Neutrophils from a patient with recurrent pyogenic infections since infancy were found to have morphologic abnormalities and impaired functions. The neutrophils had an abnormal nuclear shape, no or few secondary granules, and no alkaline phosphatase activity. Primary granules were normal in number and structure, and were positive for peroxidase. Immature granulocytes were structurally normal. The neutrophils were impaired in chemotaxis and bactericidal capacity. The patient's marrow cells formed increased numbers of granulocytic colonies of small size in culture. Her peripheral leukocytes produced elevated levels of CSA and adherent marrow cells did not inhibit colony formation. These data indicate an intrinsic neutrophil defect which allows normal proliferation of precursor cells, but results in abnormal morphogenesis and impaired function as the cells mature.