Umbilical-cord blood from unrelated donors can restore hematopoiesis in adults who receive myeloablative therapy. Transplantation of allogeneic hematopoietic stem cells, an effective treatment for hematologic cancers, 1 is limited by the availability of HLA-matched donors. The risk of severe graft-versus-host disease (GVHD) after the transplantation of bone marrow from unrelated donors or partially HLA-mismatched related donors is another drawback of the procedure. 2 – 6 Umbilical-cord blood is a source of hematopoietic stem cells that has been successfully used for transplantation, primarily in children. 7 – 17 Grafts of umbilical-cord blood reconstitute hematopoiesis more slowly than does HLA-matched marrow from a sibling or an unrelated adult donor, 2 – 6 but the incidence and severity of GVHD are lower with transplantation . . .