Hematopoietic stem cell homing and engraftment require several adhesion interactions, which are not fully understood. Engraftment of nonobese/severe combined immunodeficiency (NOD/SCID) mice by human stem cells is dependent on the major integrins very late activation antigen–4 (VLA-4); VLA-5; and to a lesser degree, lymphocyte function associated antigen–1 (LFA-1). Treatment of human CD34⁺cells with antibodies to either VLA-4 or VLA-5 prevented engraftment, and treatment with anti–LFA-1 antibodies significantly reduced the levels of engraftment. Activation of CD34⁺ cells, which bear the chemokine receptor CXCR4, with stromal derived factor 1 (SDF-1) led to firm adhesion and transendothelial migration, which was dependent on LFA-1/ICAM-1 (intracellular adhesion molecule–1) and VLA-4/VCAM-1 (vascular adhesion molecule–1). Furthermore, SDF-1–induced polarization and extravasation of CD34⁺/CXCR4⁺ cells through the extracellular matrix underlining the endothelium was dependent on both VLA-4 and VLA-5. Our results demonstrate that repopulating human stem cells functionally express LFA-1, VLA-4, and VLA-5. Furthermore, this study implies a novel approach to further advance clinical transplantation.