1. Chinchilla, Chinchilla villidera, alpha-1-antitrypsin has been purified to homogeneity and partially characterized according to mol. wt, amino acid and carbohydrate composition and N-terminal amino acid sequence (30 residues). 2. The mol. wt is between 52,000 and 55,000 as determined by PAGE or sedimentation equilibrium. 3. The best alignment between chinchilla, human and baboon alpha-1-antitrypsin amino acid sequences offsets the chinchilla sequence 6 positions vs the primate structures. 4. This alignment suggests potential importance of the sequence His-Glu-Gln-Glu-His at positions 11-15. 5. Additionally, the segment Leu-Ala-Glu-Phe-Ala, positions 25-29, is strictly conserved. 6. Shorter N-terminal sequences available for rat and rabbit alpha-1-antitrypsin appear to follow the offset alignment vs the primate structures.