Elastic fibers in 15 blebs and 17 bullae with spontaneous pneumothorax were studied by means of electron microscopy and light and electron microscopic immunohistochemistry for elastin and alpha 1-antitrypsin. Blebs were formed in association with focal organized alveoli, and bullae were formed in association with pulmonary emphysema. Both blebs and bullae had abnormal elastic fibers. Ultrastructurally, abnormal elastic fibers of blebs and bullae consisted of accumulated thick and fine fibers. Accumulated thick elastic fibers showed vacuolar changes and electron-dense granular deposits, and they were associated with spiraling collagen fibrils. These thick elastic fibers reacted evenly with antielastin antibody and also reacted with anti-alpha 1-antitrypsin antibody. They are thought to be degraded elastic fibers. Accumulated fine elastic fibers consisted of bundles of microfibrils and granular amorphous components, and they reacted with anti-elastin and anti-alpha 1-antitrypsin antibody. These fine elastic fibers are thought to be not only newly formed in the process of organization but also degraded. It is suggested that elastic fibers of blebs and bullae are degraded due to an imbalance between elastase and alpha 1-antitrypsin.