Fibronectin is a major protein of blood and tissues. It has been intensively studied because of its many interactions with cells and other macromolecules. Fibronectin is a principal component of the extracellular matrix, and its most important function seems to be in tissue remodelling during embryogenesis and wound healing. It may influence a number of other physiological processes, including phagocytosis. The concentration of plasma fibronectin and the distribution of tissue fibronectin are altered in disease states, although diseases specifically caused by quantitative or qualitative abnormalities of fibronectin have not been identified.