the prevalence of alphaantitrypsin heterozygotes pi mz in patients with obstructive pulmonary disease an increased incidence of intermediate deficiency of serum alpha1antitrypsin resulting from pi phenotype mz has been reported in patients with chronic obstructive pulmonary disease copd by some laboratories but not confirmed by others prevalence of pi mz was determined in patients with copd among 502 subjects referred to a pulmonary function testing laboratory in a region with low concentrations of air pollutants control prevalences were obtained from 930 randomly selected subjects in the same community as well as from patients without copd referred to the laboratory depending on criteria used to define copd 155 to 306 subjects had copd pi mz prevalence in subjects with copd varied from 15 to 4 times the prevalence in the community control group and in the patients without copd this difference approached significance or was significant because pi mz was present in only 35 to 45 per cent of patients with copd pi mz is not a major factor in the etiology of copd in this community the higher incidence of pi mz inpatients with copd reported by other investigators may be explained by small sample size bias in selection of study or control population groups or the development of copd from interaction between pi mz and air pollutants or other factors not present in this community