The respiratory epithelium is a potential site for somatic gene therapy for the common hereditary disorders α1-antitrypsin (α1AT) deficiency and cystic fibrosis. A replication-deficient adenoviral vector (Ad-α1AT) containing an adenovirus major late promoter and a recombinant human α1AT gene was used to infect epithelial cells of the cotton rat respiratory tract in vitro and in vivo. Freshly isolated tracheobronchial epithelial cells infected with Ad-α1AT contained human α1AT messenger RNA transcripts and synthesized and secreted human α1AT. After in vivo intratracheal administration of Ad-α1AT to these rats, human α1AT messenger RNA was observed in the respiratory epithelium, human α1AT was synthesized and secreted by lung tissue, and human α1AT was detected in the epithelial lining fluid for at least 1 week.