Recently, a close association between hematopoiesis and chemokines and their receptors has been demonstrated. Much attention has been focused on the regulation of hematopoiesis by chemokines, because of the possibility of direct consequence for clinical practice in cell therapies such as hematopoietic stem cell transplantation. This report reviews the physiological roles of chemokines and their receptors in the context of hematopoietic cell regulation, with particular focus on the involvement of stromal cell derived factor (SDF)-1/pre-B cell growth stimulating factor (PBSF) and its receptor CXCR4. The proliferation, differentiation, migration, and engraftment of hematopoietic stem cells are discussed, and thereby raise a number of unresolved problems and points-to-consider.