Before receiving allogeneic transplants--the most common type--patients with blood cancers must undergo a conditioning regimen of high-dose chemotherapy or radiation to kill any resident cancer cells, suppress the patient's immune system, and leave a disease-free environment into which healthy new blood stem cells can be infused. Known as myeloablation, the regimen prepares the patient to accept a "non-self" graft without triggering a severe attack on the patient by the transplant (graft vs. host disease).