Loss of lung elastic recoil causing hyperinflation with increased TLC and decreased diffusing capacity and expiratory airflow are physiologic hallmarks of emphysema. We studied lung mechanics in 10 patients (seven men and three women) aged 69 +/- 9 yr (mean +/- SD) who had fixed, severe expiratory airflow limitation with a mean FEV1 = 0.73 +/- 0.1 L (mean +/- SD) (32 +/- 7% predicted) and lung computed tomographic picture grade score <= 20, indicating no or trivial emphysema. Three patients died, in whom whole-lung emphysema scores were 15 each and small airways were abnormal. Marked hyperinflation was present in all 10 patients studied, with TLC 7.3 +/- 1.1 L (140 +/- 12% predicted); FRC 5.6 +/- 0.8 L (177 +/- 30% predicted); and RV 5.2 +/- 0.8 L (242 +/- 28% predicted). Diffusing capacity of carbon monoxide (DLCO was reduced, at 12 +/- 6 ml/min/mm Hg (61 +/- 29% predicted). The pressure-volume curves of the lung were markedly abnormal. Pst(L) at TLC was 11.6 +/- 1.4 cm H2O. Transdiaphragmatic pressure (Pdi) in five patients was 66 +/- 13 cm H2O. These results indicate that severe small-airways disease with no or trivial emphysema may cause a spurious reduction in diffusing capacity as well as severe loss of lung elastic recoil resulting in marked hyperinflation, increased TLC, and decreased Pdi and expiratory airflow.