Male golden hamsters were exposed to a solution of purified pancreatic elastase by intratracheal injection. They developed panlobular (panacinar) emphysema and, in addition, were found to show severe goblet cell metaplasia in the major bronchi. The metaplastic change in the respiratory epithelium was associated with persistence of a fenestrated sheet of mucus, widely present throughout the bronchial tree, which was greater in amount than that in either unexposed or saline exposed controls. Transmission electron micrography showed a striking increase in size of individual goblet cells, due to increased numbers of secretory droplets which were also much larger and paler than in control bronchi. Ciliated cells appeared smaller than normal due to compression by the swollen goblet cells. The presence of prominent dilatation of the endoplasmic reticulum and the increased frequency of secretory droplet release from the luminal surface stronly suggest that the goblet cell changes were due to increased formation and secretion of mucus into the damaged bronchi. These experiments show that a single exposure to elastase produces both severe panlobular emphysema and goblet cell metaplasia. The changes resemble several of the anatomic features of chronic obstructive lung disease in man for which this injury may be a suitable model.