Four patients with acute myelosclerosis were treated with chemoradiotherapy and bone marrow transplantation. Three of the four had prompt engraftment with greater than 0.10 X 10(9) granulocytes/liter three weeks after transplantation. One patient continues in complete remission one year after transplantation. One patient experienced a partial remission and two patients died early in the post-transplantation period. Marrow fibrosis disappeared in three of the four patients. The patient with residual marrow fibrosis died 22 days after transplantation. It is apparent that marrow fibrosis is reversible. In view of the absence of other effective therapy, intensive therapy with marrow transplantation should be considered as primary therapy for patients with acute myelosclerosis who have a suitable marrow donor.