Chemokines are important regulators of both hemopoietic progenitor cell (HPC) proliferation and adhesion to extracellular matrix molecules. Here, we compared the biological effects of the CC chemokine macrophage inflammatory protein-1α (MIP-1α) with those of the CXC chemokine stroma-derived factor-1α (SDF-1α) on immunomagnetically purified CD34⁺ cells from leukapheresis products (LP CD34⁺). In particular, studies on chemokine-induced alterations of LP CD34⁺ cell attachment to fibronectin-coated plastic surfaces, proliferation of these cells in colony-forming cell (CFC) assays and intracellular calcium mobilization were performed. MIP-1α but not SDF-1α was found to increase the adhesion of LP CD34⁺ cells to fibronectin in a dose-dependent manner. Both chemokines elicited growth-suppressive effects on LP CD34⁺ cells in CFC assays. While MIP-1α reduced the number of granulomonocytic (CFC-GM) and erythroid (BFU-E) colonies to the same extent, SDF-1α showed a significantly greater inhibitory effect on CFC-GM than BFU-E. Finally, we demonstrated that SDF-1α but not MIP-1α triggers increases in intracellular calcium in LP CD34⁺ cells. The SDF-1α-induced calcium response was rapid and concentration-dependent, with a maximal stimulation observed at ≥ 15 ng/ml. In conclusion, our data suggest distinct biological properties of SDF-1α and MIP-1α in terms of modulation of LP CD34⁺ cell adhesion to fibronectin and intracellular calcium levels. However, comparable growth-suppressive effects on HPC proliferation were observed, indicating that this feature may be independent of chemokine-induced calcium responses.