Bone marrow is the body's diffuse blod-formin tissue, contained in the cavities of bones in the adult, principally in the pelvis, breast bone, ribs and skull. The failure of this blood forming process, as in leukaemiae is lethal without treatment.

The transplantation procedure is deceptively simple. Donor marrow cells are administered to the recipient intravenously, like a blood transfusion. In days, the cells migrate to the host's bone cavities and begin to function.

But the preparation, known as the conditioning and post transplantation care are complex, and both stages carry certain grave risks to the recipient. Space is created by destroying the recipient's own marrow, using chemotherapy and total body irradiation over a period of several days. Immunosuppressive therapy is also begun pre-transplant to reduce the likelihood of rejection. After transplant, the recipient, lacking any natural immunity to infection, is nursed in strict isolation. Grafted tissue may come from anyone of sources: from an identical twin, or a relative with identical antigen types; from an unrelated donor with closely matched antigens, even from the recipient ownself. Usually it is transfused immediately, but it may be stored in a bone marrow bank.