Leukocyte extravasation from the blood into tissues is of paramount importance for normal immunosurveillance and in mounting adequate inflammatory responses. Multiple traditional adhesion molecules and chemoattractants on leukocytes and endothelial cells are involved in the emigration process. Vascular adhesion protein 1 (VAP-1) is a nonclassical inflammation-inducible endothelial molecule involved in leukocyte-subtype-specific rolling under physiological shear. Molecularly, VAP-1 belongs to a special class of cell surface amino oxidases. The enzymatic reaction itself and the biologically active end products can potentially regulate the adhesive status of the vessel wall. Thus, VAP-1 is an ectoenzyme that has inter-related adhesive and enzymatic functions in regulating physiological trafficking and inflammation.