The adhesion of cells to the extracellular matrix (ECM) protein, fibronectin, is important in the regulation and coordination of such complex processes as cell growth, migration, differentiation, and ECM organization. The deposition of fibronectin into the ECM is a cell-dependent process that is normally tightly regulated to ensure controlled matrix deposition. Increased deposition of fibronectin and collagen into the subepithelial space of the airways is observed in all forms of asthma and occurs early in the progression of the disease. Experimental evidence suggests a model in which fibronectin matrix accumulation contributes to the progression of asthma by altering both the structural properties of the airways and the functional properties of cells of the airway wall.