Fibronectin 1 (FN1) is a high molecular weight glycoprotein which exists in both a soluble form in plasma (plasma FN1) and other body fluids and an insoluble form in the extracellular matrix (cellular FN1). Plasma FN1 (dimeric form) is secreted by hepatocytes. Cellular FN (dimeric or cross-linked multimeric forms), made by fibroblasts, epithelial and other cell types, is deposited as fibrils in the extracellular matrix. FN1 binds to cell surfaces through integrins and to various compounds including collagen, fibrin and heparin. It is involved in cell adhesion and migration processes including embryogenesis, wound healing, hemostasis, host defense, and metastasis.