The utility of replication-deficient recombinant adenovirus vector-mediated transfer and expression of the alpha 1-antitrypsin (alpha 1AT) cDNA to peritoneal mesothelial tissues was evaluated as a means of delivering alpha 1AT to the systemic circulation. Preliminary studies with Ad.RSV beta gal, an adenovirus vector expressing the Escherichia coli lacZ gene (beta-galactosidase), showed that intraperitoneal injection of 10(9) plaque-forming units (pfu) to cotton rats resulted in beta-galactosidase activity in mesothelial cells lining the peritoneal cavity. After intraperitoneal administration of 10(9) pfu of Ad alpha 1AT (an adenovirus vector containing the human alpha 1AT cDNA), human alpha 1AT was detectable in serum for up to 24 days, with a maximal level of 3.4 micrograms/ml at 4 days. Expression of the exogenous gene was localized to the peritoneal mesothelium as PCR analyses detected no evidence of expression of the exogenous gene in any other tissues evaluated. Anti-adenovirus vector antibodies were detectable in serum after intraperitoneal administration of the recombinant vectors, including antibodies with neutralizing activity. Repeat administrations of adenovirus vectors to the peritoneal cavity at 1 wk and 1 mo after the initial dose failed to show gene expression, but repeat administration 3 mo after demonstrated measurable gene transfer and expression. Together these observations suggest replication-deficient adenovirus-mediated gene transfer to the peritoneal mesothelium offers a promising means to transfer alpha 1AT to the systemic circulation, although immunity induced against the adenovirus may limit frequent repetitive dosing.