The lamina propria of nasal mucosa has been thought to play a key role in function and metabolism of respiratory epithelia by allowing exchange of various substances and migratory cells from blood vessels into the epithelium. Here we show that the lamina propria of mucosa transplanted to rat rectus abdominis muscle looses its typical structure and becomes vascularized connective tissue. In the subepithelial space of free grafted respiratory epithelia nasal glands, ducts and nerves degenerate and are no more detectable 3 weeks after transplantation. By contrast the epithelial cell layer regenerates, resulting in a healthy appearing mucosa. Histological and functional controls revealed that regenerated respiratory epithelium lies on a layer of vascularized connective tissue and displays normal cellular differentiation and ciliary function. The present experiments demonstrate that the lamina propria can be replaced by vascularized connective tissue without functional loss of the overlaying epithelium. Thus the results argue against a key role of lamina propria in mucosal function.