Magnetic resonance (MR) of bone marrow was studied in two cases of acute leukemia which showed bone marrow necrosis. Case 1:A 24-year-old female was admitted because of sternum pain and bleeding tendency. She was diagnosed AML based on the peripheral blood picture. Bone marrow biopsy revealed the presence of bone marrow necrosis. T1 weighted imaging of MR showed low signal intensity in all vertebral marrow. Fatty marrow was demonstrated after achieving complete remission and the MR imaging of bone marrow changed to show high intensity, suggesting fat deposition. Case 2: A 19-year-old female suffered from chest pain and lumbago, and was diagnosed as ALL. DIC and bone marrow necrosis were confirmed during chemotherapy for remission induction. T1 weighted imaging showed the mosaic pattern of low and high signal intensity. She achieved complete remission and bone marrow clot revealed the presence of fatty marrow. Most areas of low signal intensity of T1 weighted imaging changed to those of high signal intensity. These observations suggest that necrotized bone marrow seemed to change to fatty marrow along with achieving remission. MR imaging study of bone marrow is useful for evaluating hematopoiesis in hematologic disorders.