CFTR and cystic fibrosis: These data, taken together with those indicating that overexpression of CFTR on a per cell basis was not detrimental to ion and fluid transport processes, indicate that gene delivery vectors capable of targeting at least 25% of the surface airway epithelial cells will be sufficient to restore ASL height regulation and MCT to levels comparable to those exhibited in non-CF airway epithelia and that precise regulation of CFTR levels at least in ciliated cells is not required.