Chemokine–chemokine receptor interactions are important to hematopoiesis and immune cell function, two highly interactive processes. Recent studies have clarified the role of chemokines and their receptors in regulating hematopoiesis, and agents modulating chemokines are being evaluated in preclinical and clinical studies. Examples of such efforts include inhibition of CD26 for enhanced homing and engraftment of hematopoietic stem and progenitor cells, and the use of the SDF-1/CXCL12–CXCR4 antagonist, AMD3100 for mobilization of hematopoietic stem and progenitor cells and their use for stem cell transplantation.