We measured pulmonary functions in 10 nonsmoking asymptomatic subjects, ages 40.5 years +/- 9.2 years, with alpha1 antitrypsin heterozygous deficiency (phenotype MZ). The subjects were longstanding residents of the greater Los Angeles area. The range of physiologic studies and per cent of normal predicted values were forced vital capacity (FVC), 2.8 to 7.0 liters (86 to 124 per cent predicted); ratio of the forced expiratory volume in 1 second to the FVC, 70 to 86 per cent (86 to 104 per cent predicted); the ratio of the residual volume to total lung capacity, 28 to 44 per cent (94 to 119 per cent predicted); total lung capacity, 4.8 to 9.8 liters (80 to 119 per cent predicted); flow at 50 per cent FVC, 3.1 to 7.8 liters per second (69 to 140 per cent); and volume of isoflow, 7.3 to 26 per cent of forced vital capacity (38 to 137 per cent predicted). In eight patients studied, static deflation pressure volume curves were normal, and at respiratory rate of 60 breaths/min the ratio of dynamic compliance to static compliance did not fall below 84 per cent. We have found that these nonsmoking heterozygotes with alpha1 antitrypsin deficiency have normal pulmonary functions (within 1.67 SD of predicted mean).