Recently interest has increased in using less toxic chemotherapy protocols that are termed submyeloablative. The intent is to allow partial engraftment of a donor immune and hemopoietic systems with subsequent progressive replacement of the host's own hemopoiesis and immunity. As the donor immune system becomes established, patients may develop full donor chimerism, without passing through the period of prolonged aplasia associated with conventional conditioning regimens, and with less of the associated toxicity. Preliminary results in high-risk patients have shown treatment related mortality (TRM) of 15-20%, versus 50% expected, with an overall survival rate of 70-80% at 1-2 years post transplant.