Objective. To observe the effect of granulocyte-colony stimulating factor (G-CSF) on differentiation and proliferation of CD34(+) cells from peripheral blood in presence of recombinant hematopoietic growth factor (HGF). Methods. Peripheral blood mononuclear cells mobilized by G-CSF were obtained from patients suffering from carcinoma, preparing for autologous bone marrow transplantation. CD34(+) cells were isolated by derivatized polystyrene tissue culture flask which had covalently immobilized soybean agglutinin lectin and was coated with anti-CD34 antibody; and this kind of cells were incubated in liquid culture medium for up to 28 days under the stimulation of combination of growth factors, i.e., stem cell factor (SCF) and interleukin-3 (IL-3) with or without G-CSF. The changes of nucleated cells, colony forming unit-granulocyte and monocyte (CFU-GM), burst forming unit-erythrocyte (BFU-E), colony forming unit-megakaryocyte (CFU-MK), and myeloid-associated markers were evaluated. Results. An increase of nucleated cells (mean 640-fold in crease) occurred during culture. CFU-GM production is parallel to the nucleated cell production until the 11th day (mean 82-fold increase) in combination of 3 HGF, i.e., G-CSF, IL-3 and SCF. A large number of cells expressing late myeloid markers appeared on the 11th day in suspension culture of CD34(+) cells. Conclusion. G-CSF was found to synergize with IL-3 and SCF in inducing rapid proliferation of purified CD34(+) cells and differentiation to multiple myeloid lineages. The stroma-free, cytokine-driven culture system could achieve a degree of amplification of colony forming cells, suggesting the feasibility of culture of hematopoietic progenitor cells in vitro as an adjunct to hematopoietic stem cell transplantation.