To elucidate the effect of gene transfected marrow stromal cell on expansion of human cord blood CD34(+) cells, a culture system was established in which FL and TPO genes were transfected into human stromal cell line HFCL. To establish gene transfected stromal cells co-culture system, cord blood CD34(+) cells were purified by using a magnetic beads sorting system. The number of all cells and the number of CD34(+) cells and CFC (CFU-GM and BFU-E) were counted in different culture systems. The results showed that in all 8 culture systems, SCF+IL-3+HFT manifested the most potent combination, with the number of total nucleated cells increasing by (893.3 +/-52.1)-fold, total progenitor cells (CFC) by (74.5 +/-5.2)-fold and CD34(+) cells by 15.7-fold. Maximal expansions of CFC and CD34(+) cells were observed at the end of the second week of culture. Within 14 days of culture, (78.1 +/- 5.5)-fold and (57.0 +/- 19.7)-fold increases in CFU-GM and BFU-E were obtained. Moreover, generation of LTC-IC from amplified CD34(+) cells within 28 days was found only in two combinations, i.e. SCF+IL-3+FL+TPO and SCF+IL-3+HFT, and there was no significant difference between these two groups statistically. These results suggest that human umbilical cord blood CD34(+) cells can be extensively expanded ex vivo by using gene transfected stromal cells along with cytokines.