Mucosal vascular addressin-1 (MAdCAM-1) is a type I transmembrane glycoprotein expressed at high levels on high endothelial venules (HEV) of Peyer�s patches and mesenteric lymph nodes, and on flatwalled venules within the gut lamina propria. It is also expressed on sinus-lining cells in the spleen.1-3 The countereceptor or �homing receptor� for MAdCAM-1 is alpha4beta7 integrin (also known as LPAM-1). MAdCAM-1 is also a facultative ligand for CD62L/L-selectin.4, 5 The monoclonal antibody MECA-367 binds to the first domain of MAdCAM-1 and blocks MAdCAM-1-dependent binding in vitro and lymphocyte homing to Peyer�s patch HEV in vivo.1, 2, 4