The frequency of presence of various phenotypes of alpha 1-antitrypsin was studied in 31 patients with intrinsic asthma and 11 with ASA-Triad, and compared to a group of 200 people representative of the general population. The MZ and SZ phenotype is more frequent in intrinsic asthmatics (p < 0.00001) and MZ in ASA-Triad (p < 0.0005) than in the control group. No differences were found between the intrinsic asthmatics and ASA-Triad. All the patients were divided into groups according to their clinical characteristics and an increase of the MZ phenotype was observed (p < 0.001) in patients with: nasal polyposis, intolerance to non-steroidal anti-inflammatories, a family history of atopy and peripheral eosinophilia (p < 0.01). Alpha-1-antitrypsin deficiency could be important in the pathogenesis of inflammatory processes and in the clinical manifestations characteristic of patients with intrinsic asthma and ASA-Triad.