To examine the relationship between lung structure and function, static deflation pressure-volume curves were measured post mortem in 14 normal and 7 emphysematous lungs, and the results were compared to morphometric measurements of lung. Elastic behavior was described satisfactorily by an exponential function: V = A -Be-KP, where V is lung volume, P is static recoil pressure, and A, B, and K are constants. The constant K, an index of pulmonary elasticity, was closely related to a morphometric measurement of mean alveolar size. In normal lungs the decrease in pulmonary elasticity with age was quantified by an increase in K. When emphysema was present, K was invariably increased by more than 2 SD above the mean predicted value for age, reflecting the abnormally increased distensibility of alveoli in this disorder. The present findings indicate that a similar analysis of pressure-volume measurements obtained during life will reliably detect the presence of pulmonary emphysema in patients with chronic airflow limitation.