Human umbilical cord blood cells represent a potential alternative to bone marrow as a source of stem and progenitor cells for allogeneic transplantation. Therefore, many studies are underway to evaluate the number of cord blood stem cells and their amplification potential. We analyze here the amplification potential of CD34+cord blood cells in liquid cultures stimulated with stem cell factor (SCF) in combination with interleukin-3 (IL-3), erythropoietin (Epo) or granulocyte colony-stimulating factor (G-CSF) under serum-deprived conditions. We report that under certain circumstances (stimulation with SCF and IL-3, replacing of the medium and growth factors every 3-4 days, no change of the initial culture flask, 37°C as incubation temperature), CD34+cells give rise to differentiated cells and progenitor cells for more than two months. During this period, more than 1010differentiated cells and 106progenitor cells are generated from 0.25-1×104CD34+cells in the absence of a stromal layer. These data highlight the high proliferative and differentiative potential of cord blood stem cells and, because the culture procedures are relatively simple and do not require a stromal layer, open the way to the clinical use of ex vivo stem cell expansion.