A patient receiving allogeneic bone marrow transplant for treatment of acute myelomonocytic leukemia died on the 78th post-transplant day with clinically unrecognized disseminated histoplasmosis. Granulomas and Histoplasma organisms were found in the histologic sections of the marrow aspirate. Patients from endemic areas referred to transplant centers may be at high risk for disseminated histoplasmosis when treated with long-term prednisone for graft-versus-host disease. Aspiration of bone marrow with use of clot sections is a minimally invasive, sensitive, and rapid means of detecting granulomatous infection in such febrile immunosuppressed hosts. Disseminated histoplasmosis has not been described previously as a complication of bone marrow transplantation.