Human stromal cells were immortalized and fixed with glutaraldehyde to support an ex vivo expansion of human cord blood hematopoietic progenitor cells. In addition, this enabled glutaraldehyde-fixed stromal cells to be stored at VC. Although freeze-dried glutaraldehyde-fixed stromal cells did not increase the number of the progenitor cells, the percent decrease in the number of CD34(+) cells in the presence of freeze-dried glutaraldehyde-fixed stromal cells was less than that in the absence of the stromal cells. Thus, glutaraldehyde-fixed stromal cells can serve as a stabilizing device for hematopoietic cell expansion.