Male hamster weighing 100-140 g were exposed to 50-500 microgram purified elastrase per 100 g body weight by intratracheal injection. The hamster were killed at intervals up to 12 months after treatment, and their lungs were examined grossly and microscopically. At 8 days after treatment, the lungs appeared to have a greater volume than the controls. At 16 days, the lungs remained inflated when the pleural cavity was opened. Alveolar size was increased in proportion to the dose of elastase. From 16 days onward, the emphysematous lesion was well established. The number of goblet cells in the bronchi also increased. Counts of goblet cells as a proportion of all bronchial lining cells showed that goblet cells more than doubled in number in elastase treated hamsters as compared with controls. The mechanism for the two lesions caused by elastase was not clear. It was concluded that the elastase treated hamster is a useful model for studies of the pathogenesis of chronic bronchitis and emphysema in man.