You will receive the chemotherapy drug fludarabine for 5 days (Days 1 to 5). The drug melphalan will be given on Days 4 and 5. You may also receive the drug anti-thymocyte globulin (ATG) on Days 4, 5, 6. This will be followed by infusion of blood stem cells or bone marrow from a donor on Day 7. A separate consent will be provided to the donor. The donor can be a brother, sister or another family member or a compatible unrelated donor. The drugs and the stem cells will be given through a catheter (a small tube) placed under the collarbone. You may receive your treatment on an inpatient or outpatient basis. If treated on an inpatient basis, you will stay in the hospital during treatment and recovery, which can take 4 to 5 weeks even if there are no complications.