Hematopoietic progenitor/stem cell homing to the bone marrow requires the concerted action of several adhesion molecules. Endothelial P-and E-selectins play an important role in this process, but their ligands on a large subset of neonatederived human CD34 ؉ cells are absent, leading to a reduced ability to interact with the bone marrow (BM) microvasculature. We report here that this deficiency results from reduced ␣1,3-fucosyltransferase (