As part of a larger investigation of factors associated with chronic obstructive pulmonary disease among Yugoslavian men, an attempt was made to measure the role played by alpha1-antitrypsin deficiency in the causation of those diseases. Almost 3,000 men from Tuzla, an industrial and mining center in central Bosnia, were screened for alpha1-antitrypsin deficiency. Twenty-six men heterozygous for the Pi MZ phenotype were found in this population. The men with the Pi MZ phenotype were compared with a random sample from the total population. The analysis of the data showed that there is an apparent physiologic impairment associated with Pi Z heterozygosity that produces a shift in the relationships between the different lung volumes without over-all hyperinflation, namely, an increase in residual volume at the expense of vital capacity. However, because of the low prevalence of the Pi Z gene, it does not appear to account for much of the high rate of chronic obstructive pulmonary disease found in this population.