Donor granulocytes, obtained by filtration leukophoresis, were labeled with In-111-oxine and injected into seven severely neutropenic patients. All patients were febrile, and presumed to have infection, although infection was eventually proved in only five. Excellent demonstration of infection was achieved in two patients, and fair localization in one. One negative scan became positive when repeated with sedimentation-derived cells from a different donor. This method may be useful in detecting infections in neutropenic patients.