Adeno-associated virus type 2 (AAV) vectors have been used for gene expression in respiratory epithelial cells and may be useful in gene therapy for diseases like cystic fibrosis (CF) which affect the airways. The AAV p5 promoter together with the AAV inverted terminal repeat (ITR) forms a 263-base pair cassette which mediated efficient expression in a CF bronchial epithelial cell line. We report here that the ITR itself can mediate gene expression. In stable transfection assays, AAV-CF vectors expressing the full-length cystic fibrosis transmembrane conductance regulator (CFTR) cDNA from either the p5 promoter or the ITR restored cAMP regulation of the chloride efflux characteristic of CFTR function. An AAV-ITR-CF vector deleted for the amino terminus of CFTR was also functional. This vector was packaged into AAV particles and used to transduce cells without selection. Transduced cells also exhibited cAMP-regulated Cl- efflux. The complemented cell lines showed increased levels of CFTR protein immunofluorescence, and the presence of intact AAV-CF vector sequence was confirmed by Southern blot analysis of rescued vector sequences. These studies provide novel insights into AAV gene expression, and this newly described promoter allows for the production of AAV vectors expressing CFTR in those differentiated cells affected in CF.