Elastin is an extracellular structural protein that is critical to the expansile properties of the aorta and lung. Lung elastin synthesis is primarily limited to the late fetal and early neonatal stages of development and is minimal in normal adult lungs (1, 2). Once the protein has been produced and crosslinked, there is normally very little turnover of elastin (2). The major sources of pulmonary alveolar elastin are thought to be the smooth muscle cells of the terminal airways and the interstitial myofibroblasts (1, 3). Itis unclear why elastin synthesis is limited to a particular developmental stage and to a minority of the types of cells found in the lung. However, investigations using several