In this study, the effects of bone marrow endothelial cell conditioned medium (BMEC-CM) on hematopoietic progenitors and the expression of cytokines mRNA of BMEC were investigated. BMEC-CM was ultrafiltrated in Centriprep-10, an ultrafiltering concentrator. The retentate (MW>10 kD) and filtrate (MW<10 kD) were obtained. The effects of different components of BMEC-CM on the murine hematopoietic progenitors were examined. The results showed that the retentate of BMEC-CM (MW>10 kD) significantly promoted the growth of CFU-GM, CFU-E, BFU-E, CFU-Meg and HPP-CFC, while the growth of CFU-GM, CFU-E, BFU-E, CFU-Meg and HPP-CFC were markedly inhibited by the filtrate of BMEC-CM (MW<10 kD). The effects of BMEC-CM were dose-dependent. The presence of mRNAs for GM-CSF, TGF-beta, bone morphogenetic protein 2A, basic fibroblast growth factor receptor, endothelin-2, macrophage-stimulating 1 (MSP-1), thymosin-beta10, connective tissue growth factor, macrophage inflammatory protein 2 alpha (MIP-2alpha), IL-6, IL-11, IL-13 and IFN-gamma mRNA were successfully detected by Atlas Arrays.