High doses of cancer chemotherapy and/or radiation therapy, used prior to bone marrow or cord blood transplantation to eliminate the recipient’s blood-forming cells. Very high doses of drugs and/or radiation are used to eliminate as many diseased cells from the recipient’s marrow as possible. As a result, the recipient’s normal blood cells are also destroyed. Preparative regimens temporarily make patients immunodeficient, anemic, and platelet deficient. Immunocompetence and the ability to form red cells and platelets are restored to patients when the donated stem cells they receive engraft, i.e., begin to repopulate and reproduce in the marrow. Also known as conditioning regimen.