Interest in umbilical cord blood as an alternative source of hematopietic stem cells is growing rapidly. Umbilical cord blood offers the clinician a source of hematopoietic stem cells that are readily available and rarely contaminated by latent viruses. Moreover, the collection of umbilical cord blood poses no risk to the donor. There is no need for general anesthesia or blood replacement and the procedure causes no discomfort. Current clinical experience suggests that the incidence of GVHD in umbilical cord blood transplantation is low. These results and associated laboratory findings pose intriguing possibilities for the future of umbilical cord blood stem cells in the setting of unrelated donor transplantation. There are other intriguing possibilities for example cord blood may be an optimal source of pluripotential stem cells for use in genetherapy.