The published experience of allogeneic bone marrow transplantation for primary myelofibrosis (PMF) is limited. Three patients (24-49 years) with PMF received allogeneic marrow grafts from HLA-identical sibling donors after conditioning with 110 mg/m2 melphalan and 1050 cGy total-body irradiation (TBI). Donor marrow was not depleted of T cells, and graft-versus-host disease (GVHD) prophylaxis comprised cyclosporine and methotrexate. None of the patients was splenectomized prior to the transplant. Two patients received G-CSF post-transplant to hasten neutrophil recovery. One patient died of multi-organ failure 23 days post-transplant. Hematopoietic recovery was relatively slow in the other two who had gradual resolution of the marrow fibrosis over several months. One of the two died of overwhelming pneumococcal sepsis within 2 weeks of stopping prophylactic penicillin 31 months post-transplant. The other patient is alive and well 20 months post-transplant with a Karnofsky score of 100% and no fibrosis of the marrow. We conclude that PMF is correctable by allogeneic BMT. Hematologic recovery post-transplant is slow, but counts may normalize with time without the need for splenectomy.