Stromal cell-derived factor 1 alpha (SDF-1α) is a member of the CXC group of chemokines that binds to the G-protein coupled receptor, CXCR4, to regulate migration, proliferation, differentiation, and survival of many cell types including hematopoietic stem cells, B cells, and T cells. It is produced by bone marrow stromal cells, osteoblasts, endothelial cells, and neuronal cells. SDF-1α was first identified as the pre-B-cell growth-stimulating factor (PBSF) in the mouse bone marrow-derived stromal cell line, PA6, in the growth of B cell precursors (Hayashi et al.). SDF-1α primarily regulates cell motility during development and adulthood, including the homing of hematopoietic stem cells and neutrophils to fetal bone marrow during ontogeny (Ara et al. 2003a) and the recruitment of endothelial progenitor cells from bone marrow during angiogenesis in adulthood (Zheng et al.). In addition to its role in hematopoiesis, the SDF-1α/CXCR4 signaling pathway is also essential for the homing of primordial germ cells to gonads (Ara et al. 2003b), the migration of granule cells in the cerebellum during neurogenesis (Zou et al.), and the migration of breast cancer cells to sites of metastasis (Muller et al.).