The effects of concentrations of murine stromal and hematopoietic cells on their three-dimensional coculture in nonwoven fabrics were investigated for the construction of an ex vivo expansion system for hematopoietic progenitors without adding expensive cytokines. The increase in initial stromal cell concentration from 0.4 x 10(5) to 2.7 x 10(5) cells/ml increased progenitor concentration, while the increase in initial hematopoietic cell concentration from 0.6 x 10(5) to 6.1 x 10(5) cells/ml decreased the fold increase in hematopoietic cell concentration.