The elastic behavior of postmortem human lungs was studied in an effort to differentiate the effects of normal aging from those of mild emphysema. Static pressure volume (P V) curves were measured in 50 lungs obtained from men 15-85 yr of age, including 12 lungs with mild to moderate emphysema. The emphysema was quantitatively assessed by gross and microscopic methods. The P V relation in all lungs is accurately described by the empirically fitted equation, P = α1e (sup α2V). This expression is useful because the 2 parameters separate the effects of elastic behavior (α1) from size (α2) on the P V curve. There is a close negative correlation (R= -0.94) between age and α1 in normal lungs but no significant age dependence of α2. Further decreases in α1 are found in most emphysematous lungs.