A distinctive, hitherto undescribed lesion was found in histologic sections of aspirated bone marrow particles in five patients. The lesion occurred in close relation to lymphoid follicles, vessels, and sinusoids. It consisted of collections of cells with regular, spindle-shaped nuclei and poorly defined cytoplasmic borders. Among these cells, which were interpreted as histiocytic and/or fibroblastic elements, there were abundant eosinophils, often in aggregates (eosinophilic abscesses), plasma cells, and a few mast cells. Four of the patients were anemic, and all took numerous drugs including ampicillin, procainamide, and allopurinol. In four patients, the anemia remitted after the suspected drug was discontinued. Repeated bone marrow aspirates in three showed only an increased number of eosinophils around lymphoid follicles and blood vessels in two patients and complete disappearance of the lesion in one. Hodgkin’s disease, eosinophilic granuloma, Kaposi’s sarcoma, and lipid granuloma were considered in the differential diagnosis and were ruled out by histologic and clinical considerations.