Native pancreatic elastase and guanidinated elastase have similar in vitro and in vivo properties and produce emphysema of similar severity in hamsters. 14C-guanidinated pancreatic elastase (16,000 cpm/0.2 mg) was instilled into the trachea of anesthetized hamsters. Within 24 hours the radiolabel found in the lungs rapidly decreases to 12% of the original 16,000 cpm and to 1% after 96 hours. Most of the radiolabel and elastase activity found in the lungs can be removed by bronchopulmonary lavage up to 48 hours after installation. Although seemingly very small, there is a significant amount of radiolabel (1-2%) which cannot be removed from the lungs by extensive bronchopulmonary lavage.