The present invention provides methods for expanding human umbilical cord blood stemcells and methods for stimulating growth factor production by cord blood stemcells using an in vitro cell culture system comprising a lithium salt. The presentinvention also provides in vivo methods for enhancing the survival and growthof transplanted cord blood stem cells by treating the cells with a lithium saltprior to transplantation. In vivo methods for reducing rejection of transplanted cordblood stem cells by administering a lithium salt after transplantation are alsoprovided.