The purpose of the present study was to investigate the biological mechanism for modulating granulocytopoiesis by Panax ginseng. The techniques of culture of hematopoietic progenitor cells and hematopoietic stromal cells in vitro, biological assay of hematopoietic growth factor (HGF), immunocytochemistry, in situ hybridization of nucleic acid, immunoprecipitation and Western blot were used to explore the effect of total saponins of Panax ginseng (TSPG) on the expression of human granulocyte-macrophage colony stimulating factor (GM-CSF) and granulocyte-macrophage colony stimulating factor receptor alpha (GM-CSFRalpha). The results indicated that (1) bone marrow stromal cell (BMSC), thymocyte (TC), splenocyte (SC), endothelial cells (EC), and monocyte (MO) conditioned media prepared with TSPG (50 microg/ml) could significantly enhance the proliferation of CFU-GM; (2) the expressions of GM-CSF in protein and mRNA level in BMSC, TC, SC, EC and MO induced by TSPG (50 microg/ml) were much higher than that of the control; (3) the expression of GM-CSFRalpha protein in hematopoietic cells induced by TSPG (50 microg/ml) was stronger than that of the control; (4) TSPG (50 microg/ml) could stimulate the transient tyrosine phosphorylation of GM-CSFR and Shc protein. We speculate that TSPG may directly and/or indirectly promote the stromal cells and lymphocytes to produce GM-CSF and other cytokine and induce bone marrow hematopoietic cells to express GM-CSF receptors (GM-CSFRalpha), leading to the regulation of the GM-CSFR-mediated signals transduction pathway and the proliferation of human CFU-GM.