Bone marrow transplantation done to rescue patients from lethal radiation or chemotherapy or to replace abnormal marrow. Bone marrow grafts are derived from syngeneic, allogeneic, autologous, or umbilical cord sources. Transplantation of peripheral blood stem cells has been considered the favorable source for autologus stem cell transplantation over bone marrow in many highly specialized centers. More recently, umbilical cord blood has been investigated as an alteranative source for hemopoletic stem cell transplantation.