We have purified, cloned and characterized kallistatin, a tissue kallikrein-binding protein (KBP) in humans and rodents. Kallistatin is a unique serine proteinase inhibitor (serpin) with Phe-Phe residues at the P2 and P1 positions. Structural and functional analysis of kallistatin by site-directed mutagenesis and protein engineering indicate that wild-type kallistatin is selective for tissue kallikrein. Kallistatin is expressed and localized in endothelial and smooth muscle cells of blood vessels and has multiple roles in vascular function independent of the tissue kallikrein-kinin system. First, kallistatin induces vasorelaxation of isolated aortic rings and reduces renal perfusion pressure in isolated rat kidneys. Transgenic mice overexpressing rat kallistatin are hypotensive, and adenovirus-mediated gene delivery of human kallistatin attenuates blood pressure rise in spontaneously hypertensive rats. Second, kallistatin stimulates the proliferation and migration of vascular smooth muscle cells in vitro and neointima formation in balloon-injured rat arteries. Third, kallistatin inhibits the proliferation, migration and adhesion of endothelial cells in vitro and angiogenesis in the rat model of hindlimb ischemia. These results demonstrate novel roles of kallistatin in blood pressure regulation and vascular remodeling.