Few studies have explored bone marrow findings in patients with graft failure or delayed engraftment after bone marrow transplantation (BMT). The authors retrospectively identified 4 patients of 165 transplant recipients who underwent bone marrow examination after BMT because peripheral blood counts had not recovered to expected levels. All patients were women who were 21- to 49-years old (mean 37 years). Three patients underwent autologous BMT; the fourth received peripheral stem cell infusion. Transplants were performed for treatment of Hodgkin's disease, breast carcinoma, and follicular small cleaved cell lymphoma. Three patients received GM-CSF after marrow infusion. The time between transplant and biopsy ranged from 19 to 40 days (mean 22 days). White cell counts ranged from 0.1 to 0.6 x 10(9)/L, hematocrits from .25 to .41, and platelet counts from 10 x 10(9)/L to 39 x 10(9)/L. Aspirate smears were markedly hypocellular in all cases, and markedly hypocellular, and all contained histiocytes with foamy eosinophilic cytoplasm diffusely throughout the biopsy. Acid-fast and Gomori's methenamine-silver (GMS) stains were negative. Serous fat atrophy and marrow fibrosis were not seen. Delayed engraftment after BMT may be associated with a profuse histiocytic proliferation similar to that seen in immunodeficiency, some hematologic disorders, and storage diseases.