Part II demonstrates the results of MRI follow up studies of 23 children with leukemia. Differentiation between leukemic cells and normal hematopoiesis by MRI is impossible. The state of disease can only be determined together with bone marrow biopsy. Clinical remission precedes the normalization of bone marrow signal by weeks. In non-responders, however, cytological findings and MRI findings seem to correlate at the same time. During therapy, areas of osteonecrosis may develop. They do not necessarily contradict continuing complete remission. But this does not affect the prognosis and complete remission is still a possibility. Diagnosis of relapse by MRI is only possible in correlation with studies during the different states of disease especially at clinical remission.