Patients receive buthionine sulfoximine IV as a bolus over 30 minutes followed by a 72-hour continuous infusion beginning on day -4; melphalan IV over 15 minutes on days -3 and -2; autologous peripheral blood stem cells or bone marrow IV over 15-30 minutes on day 0; and filgrastim (G-CSF) subcutaneously or IV once daily beginning on day 0 and continuing until blood counts recover.