Ectonucleoside triphosphate diphosphohydrolase-1(NTPDase-1)is an integral membrane protein with an extracellular active site. Recombinant mouse NTPDase-1wasexpressed as a protein lacking its N- andC-terminaltransmembrane domains, resulting in the secretion of the soluble ectodomain. NTPDase-1was originally describedas CD39, a B lymphocyte cell surface marker. but it is also present on the surface of natural killer cells, T cells, and some endothelial cells. NTPDase1hydrolyzes the β-andγ phosphate residues of nucleotides, preferring ATP as the substrate. Through its hydrolysis of extracellular nucleotides, NTPDase-1plays arole in the regulation of purinergic signaling. NTPDase-1is involved in the processes of thromboregulation and vascular inflammation. The administration ofsoluble NTPDase-1may have therapeutic applications for the treatment of some vascular and transplantation-associateddiseases.