Umbilical cord blood (UCB) is increasingly being used as a donor source of hematopoietic stem cells (HSCs) to treat blood malignancies. The main limitation to the widespread use of UCB is the low number of HSCs per unit. To compensate, a strategy of in vitro stem cell amplification has been attempted in different research laboratories. The major hurdle blocking success is the creation of culture conditions that support the growth of hematopoietic stem cells without their differentiation. We have designed a simple culture system for stem and progenitor cell expansion that resulted in an increased number of hematopoietic stem cells that maintain their ability to home to the bone marrow and to permanently engraft.