Laurel and Eriksson published the first report indicating that alpha 1-antitrypsin deficiency predisposed patients to the development of Chronic Obstructive Pulmonary Disease (COPD). For the purpose of early detection, disturbances of pulmonary function in alpha 1-antitrypsin mild deficiency cases (PiMZ) were compared with those of normal cases (PiMM) in caucasian Americans. The marked results are as follows. 1) Parameters of flow-volume curves were more disturbed in PiMZ cases than in PiMM cases. 2) Volumes of isoflow are specially different between PiMZ and PiMM cases. 3) Mechanical properties, like lung work of breathing, were larger in PiMZ cases than in PiMM cases.