Vitronectin is an abundant 75 kDa glycoprotein found in serum and the extracellular matrix. It binds numerous cellular components including collagen, plasminogen, heparin, and plasminogen activator inhibitor-1. Vitronectin promotes cell adhesion and spreading, inhibits the membrane-damaging effect of the terminal cytolytic complement pathway, and may have roles in wound healing and tumor progression.