Neutrophils from a patient with lactoferrin deficiency were examined and the quantity and subcellular localization of protein markers were determined on Percoll density gradients. Distribution of azurophilic and specific granule markers was abnormal in that azurophilic granules were lighter than normal and appeared in the fraction of the gradient where normally the specific granules sediment. The specific granule membrane markers, cytochrome b-235 and its associated flavoprotein, were abnormally distributed in the gamma fraction, the site of the plasma membrane marker alkaline phosphatase. Thus, the b-cytochrome-flavoprotein complex had either been incorporated into the plasma membrane or was still present in the membranes of granules that were abnormally light and cosedimented with the plasma membranes. This is of particular interest in regard to the patient's respiratory burst oxidase function, since the b-cytochrome/flavoprotein complex normally translocates from the specific granules to the plasma membrane to constitute the active respiratory burst oxidase. The functional consequences of this abnormal distribution are discussed, as is the importance of characterizing both intragranular enzymatic markers and granule membrane proteins to define granular disorders.