Thirty cases, including 20 autopsied, of chronic bone marrow failure, myelosclerosis and osteosclerosis have been presented and compared with similar reports in the literature. The bone marrow histopathologic sequence observed involved repeated necrobiosis of maturing hematopoietic cells, followed by overgrowth of marrow reticulum and frequent ossification. Immature erythrocytes and leukocytes were often found in the circulation, and extrameduallary hematopoiesis was characteristic. One case was complicated by leukemia. Etiologic factors implicated included exogenous toxic chemicals, liver dysfunction, endocrine abnormalities, blood loss or destruction and cardiovascular disease. Suspicion was directed toward the pathogenetic importance of protracted bone marrow exposure to certain substances normally conjugated rapidly in the liver and excreted.

ACKNOWLEDGMENT The authors acknowledge gratefully the continued assistance of Dr. John Norcross and Dr. Donat P. Cyr of Lahey Clinic, Boston, who permitted use of material from living cases. We are indebted to Dr. Shields Warren, New England Deaconess Hospital, Boston, for permission to review 10 cases; to Dr. Olive Gates, Harvard Medical School, for advice and assistance with 7 cases, including material from the Collis P. Huntington Hospital; to Professor William Boyd for 5 cases from Banting Institute, Toronto; to Dr. Paul D. Rosahn, New Britain General Hospital, New Britain, Conn., and Dr. William Dameshek for one case; to Dr. A. J. Blanchard for several cases from Christie St. Hospital, Toronto; to Drs. Lorne Whittaker and Sabin of St. Catherine’s Hospital for one case; and to Dr. John Brownlee for hematologic studies from one case.