Six patients with acute non-lymphocytic leukemia underwent autologous transplantation of circulating stem cells collected during remission. They were given cyclophosphamide (120 mg/kg) and total body irradiation (1,000-1,200 rads) (five patients) or busulfan (16 mg/kg) and melphalan (140 mg/m2) before the transfusion of 6.7 X 10(8) nucleated cells/kg corresponding to 19.7 X 10(4) CFU-GM/kg. Granulopoietic engraftment was observed in every case and was influenced by the number of CFU-GM injected. Megakaryocytic recovery was obtained in four cases.