Six children with severe congenital neutropenia and repeated life- threatening infections were investigated by examining clinical features and myeloid cell ultrastructure, cytochemistry, and in vitro proliferation. Despite the presence of neutropenia, normal numbers of colony-forming cells (CFC) were present in blood and marrow specimens, and colony-stimulating activities (CSA) from blood cells and serum were normal or slightly increased in all patients. In vitro maturation of the progenitors to neutrophils was also uniformly present in the colonies. No patients had demonstrable antineutrophil antibodies or serum inhibitors of myelopoiesis. Serum lysozyme levels were normal. Ultrastructural and cytochemical studies of directly sampled marrow cells revealed several abnormalities in most neutrophilic myeloid cells from each of the patients consistent with an intrinsic myeloid precursor cell defect. These included (1) the defective synthesis or degeneration of primary granules, (2) an absence or marked decrease of secondary granules in the few late neutrophils observed in the bone marrow, and (3) the presence of autophagy. Phagocytosis of intact myeloid cells with subsequent degeneration was not observed; however, neutrophil debris was evident in phagocytic vacuoles of marrow macrophages. Our demonstration of ultrastructurally dysmorphic neutrophilic granulocytes, intramedullary cell lysis, normal stem cell numbers, and negative serology is comparable to similar observations of erythroid cells from patients with congenital dyserythropoietic anemia. We therefore hypothesize that the dysgranulopoiesis in these children results in neutropenia and propose the descriptive name congenital dysgranulopoietic neutropenia.