Patients receive oral busulfan every 6 hours for 16 doses on days -5, -4, -3, and -2. Patients receive etoposide IV over 4 hours on days -4, -3, and -2. Bone marrow is reinfused 36-48 hours after the last dose of etoposide. Patients receive filgrastim (G-CSF) IV daily beginning 2-4 hours after bone marrow reinfusion until hematopoietic recovery.