Alpha-1-antitrypsin is a relatively common genetic deficiency that results in early emphysema. The liver as the natural source of most alpha-1-antitrypsin synthesis was the target organ selected for gene replacement therapy studies. Previous work used recombinant retroviral vectors that encode the human alpha-1-antitrypsin cDNA for ex vivo and direct in vivo transduction of hepatocytes in dogs and rodents. This approach led to low levels of human protein in the serum of recipients. In this study, recombinant adenoviral vectors that express the human alpha-1-antitrypsin cDNA under the transcriptional control of the phosphoglycerate kinase (PGK) or RSV-LTR promoters have been constructed and used for the direct transduction of mouse hepatocytes in vivo. The animals transduced with the recombinant adenoviral vectors had therapeutic serum levels of human alpha-1-antitrypsin of up to 700 micrograms/mL. Thus, adenovirus-mediated gene transfer of the hAAT cDNA into the liver was able to produce therapeutic serum concentrations of protein.