Abstract: Methods for increasing the number of human hematopoietic precursor cells in vitro are provided. The methods generally comprise (a) separating human hematopoietic precursor cells from mature hematopoietic cells present in a blood product; (b) inoculating the separated precursor cells into a culture vessel containing a culture medium comprising a nutritive medium and a source of growth factors at a density of between 1.times.10.sup.3 cells/ml and 4.times.10.sup.6 cells/ml; and (c) culturing the cells under conditions and for a time sufficient to increase the number of precursor cells relative to the number of such cells present in the blood product. The culture medium may also include a suitable amount of microcarrier beads. Suitable blood products include bone marrow, umbilical cord blood, and peripheral blood. A device for carrying out such methods is also provided.