The major limitations of cord blood transplantation(CBT)for adults have been higher rates of engraftment failure and early mortality. The amelioration of conditioning regimens could contribute to the recent improvement of early mortality in CBT. Although total body irradiation(TBI) -based regimens have remained the preferred regimens for CBT in younger patients, engraftment and survival after myeloablative intravenous busulfan-based regimens have also been improved by the addition of low-dose TBI, and/or other chemotherapeutic drugs, particularly for elderly patients. Intensified conditioning regimen could also improve engraftment and survival after CBT. To clarify whether conditioning treatment based on granulocyte-colony stimulating factor (G-CSF) priming effect improves results of CBT, a multicenter randomized phase III study is under way in Japan.