Abstract: The molecular mechanism of homing of haemopoietic stem/progenitor cells is beyond understanding.Recent years,however,it have been found that a chemokine or chemoat-tractant stromal cell-derived factor 1 (SDF 1) and its ligand CXCR4 receptor may involve in the process of transendothelial migration and adhere to bone marrow stromal cells.It may play key role in homing of haemopoietic stem/progenitor cells.