Endothelial cell-selective adhesion molecule (ESAM) is a 55-kD membrane protein composed of two extracellular Ig domains, a single transmembrane domain, and a cytoplasmic domain. ESAM is predominantly expressed at endothelial junctions and on platelets, participating in the migration of neutrophils through the vessel wall by influencing endothelial cell contacts. It impacts vascular permeability and extravasation process. Recently, it was reported that ESAM is a novel marker for murine hematopoietic stem cells (HSCs) in fetal liver. ESAM expression is correlated with HSC activity. The ESAMHi population was highly enriched for multipotent myeloid-erythroid progenitors and primitive progenitors with lymphpoietic activity, and exclusively reconstituted long-term lymphohematopoiesis in lethally irradiated recipients.