Perfosfamide is the active metabolite of the nitrogen mustard cyclophosphamide with potent antineoplastic and immunosuppressive properties. Perfosfamide alkylates DNA, thereby inhibiting DNA replication and RNA and protein synthesis. The incubation of normal human marrow cells with perfosfamide has a toxic effect on granulocyte-macrophage progenitor cells that is dose as well as white blood cell concentration dependent. It is likely that this dependency of the perfosfamide stem cell effect is caused not only by the target white blood cell concentration but by the suspension’s total protein concentration. Autologous bone marrow transplantation with perfosfamide purging in patients with acute myeloid leukemia in second complete remission produced results similar to that reported with allogeneic bone marrow transplantation. Perfosfamide had been in phase III clinical trial for the treatment of acute myeloid leukemia. However, this development was discontinued.