Conditioning regimens for allogeneic bone marrow transplantation are designed to eradicate malignant cells and to provide sufficient immunosuppression for engraftment of donor marrow. Total body irradiation and high-dose cyclophosphamide are the most established immunosuppressive agents used for this purpose. It is uncertain whether other alkylating agent-based conditioning regimens are sufficiently immunosuppressive to allow engraftment of allogeneic marrow. We report four patients who had prompt engraftment after conditioning with melphalan-based chemotherapy regimens (BEAM or busulfan/melphalan). Two patients survived without disease for a prolonged period, indicating that these melphalan regimens are sufficiently immunosuppressive to allow sustained engraftment and donor hematopoiesis.