Five hundred patients undergoing complete medical examination, and 225 consecutive patients with abnormal pulmonary function tests were studied for alpha1-antitrypsin deficiency. Within the first group, respiratory disease was diagnosed significantly more often in patients with a variant Pi phenotype (MS, MZ, FF) than in the patients with the most common phenotype, MM. Furthermore, the frequency of heterozygosity (MS or MZ) was greater in the patients who had respiratory disease. When the first and second groups were compared, the prevalence of the variant phenotypes was not statistically different.