A cDNA encoding the complete open reading frame of murine alpha 1-antitrypsin has been cloned and sequenced. The nucleic acid and predicted amino acid sequences show homology to human alpha 1-antitrypsin and demonstrate the preservation of critical structural determinants for intracellular targeting, carbohydrate attachment, and catalytic function. The alpha 1-antitrypsin gene locus (Aat) has been localized on murine chromosome 12E----F by in situ hybridization.