Chemiluminescence can be used to identify defects in the oxidative metabolism of granulocytes. This procedure has recently been adopted for use with microliter quantities of whole blood, appropriate for prenatal or neonatal study. Although the contribution of myeloperoxidase to the chemiluminescence assay has been noted, the possible diagnostic confusion between chronic granulomatous disease of childhood (which is rare and severe) and myeloperoxidase deficiency (which is common and of little clinical consequence) has not been stressed. We report a father and his infant daughter whose cells emitted no light in the luminol-enhanced luminescence assay; both patients are totally peroxidase deficient. These results emphasize the hereditary nature of myeloperoxidase deficiency, and the possibility for erroneous diagnosis of chronic granulomatous disease of childhood based on the luminol-enhanced luminescence test.