Chemotaxis responses of CFU-MK in response to various concentrations of SDF-1. CD34⁺ cells were seeded in serum-free liquid culture containing SCF and PEG-rhuMGDF for up to 6 days. After 6-day culture, the cells were subjected to chemotaxis through 5-μm pores and plated in CKU-MK assay. Results are shown of one representative experiment performed in triplicate. Two other experiments gave similar results.*P < .05, **P < .01 when compared with control.