Pulmonary function was studied in thirteen individuals heterozygous for the alpha 1-antitrypsin allele PiF. Respiratory symptoms were present in seven out of twelve individuals with the FM phenotype, of which five had pulmonary function impairment, mostly of the obstructive type. One patient with the phenotype FZ had bronchitic symptoms and a mild obstructive spirometry pattern. The results suggest a relationship between the PiF allele and chronic obstructive pulmonary disease, which is independent of the serum alpha 1-AT level.