Severely neutropenic patients who are suspected of having circulating autoantibodies to neutrophils and/or myeloid precursors present a diagnostic problem. This report describes the use of a simple bone marrow immunofluorescence test (BMIFT) to demonstrate autoantibodies reactive with the patient's own bands, neutrophils and myeloid precursors represented on fresh-frozen bone marrow aspirate smears. Positive results were seen in two of 13 evaluable marrows from children with primary neutropenia and in eight of 44 evaluable marrows from adults with primary or secondary neutropenia. The BMIFT is simple enough to perform in most laboratory environments and provides serological information to support a diagnosis of immune neutropenia when other means of investigation are precluded.