A population (n = 526), consisting of employees with COPD, was compared with 2 control populations for the prevalence of Pi-phenotypes. In the patient group, the proportions of ZZ, SZ and MZ were significantly elevated. Among the patient population a prospective study was carried out to evaluate the role of alpha 1-antitrypsin deficiency as a cofactor in COPD. Severity of disease was estimated by standard pulmonary function tests, X-ray signs for emphysema and clinical assessment. Patients with ZZ, SZ and MZ were significantly worse than their MM partners. An influence of MS cannot be rejected. Phenotyping of all patients with COPD is advocated. Screening can also be by determining the ratio of alpha 1-antitrypsin and acid alpha 1-glycoprotein concentrations, which allowed detection of all ZZ, SZ, MZ and about 60% of the MS patients.