In a community survey in Oslo, Norway, comprising 1268 persons, alpha 1-antitrypsin concentration in serum (AT) and protease-inhibitor (Pi) phenotypes were examined in 1258 subjects. Estimated percentage distribution of Pi-phenotypes in the target population aged 15--70 years was M 87.30%, MS 4.65%, MZ 4.73%, FM 2.69%, SZ 0.13%, IM 0.20%, FZ 0.07%, S 0.06%, FS 0.07% and Z 0.06%. The distribution curve of AT had a normal (Gaussian) shape and the ranges of AT demonstrated great overlap of types MS and MZ with type M. In subjects with phenotype MZ neither respiratory symptoms nor physicians' diagnoses of chronic obstructive lung disease (COLD) were more frequent than in M subjects. Physicians' diagnoses of COLD were slightly more frequent (0.06 greater than P greater than 0.01) in subjects with phenotype MS than M, probably due to there being more smokers in the MS group. Spirometric variables given as per-cent of predicted values yielded large differences between smokers and non-smokers but no differences among phenotypes M, MS and MZ. Radiologic signs of hypertransradiancy and/or emphysema were evently distributed in M, MS and MZ subjects. The only subject observed with Pi-type Z and one out of three subjects with type SZ had COLD. In neither smokers nor non-smokers is phenotype MZ a risk factor of clinical importance for development of obstructive lung disease.