1. It is appropriate to label patients with chronic airway obstruction as having chronic obstructive bronchopulmonary disease until a more precise diagnosis can be made. Asthma can usually, but not always, be detected by a history of episodic, non-effort-dependent dyspnea with wheezing.2. When patients with chronic obstructive bronchopulmonary disease die with the clinical picture of secondary polycythemia and recurrent right heart failure, chronic bronchitis is apt to be a major morphologic finding.3. Bronchitis and emphysema are often coexistent, but may be sorted out, when one is predominant, by means of various clinical and physiological features dependent to a large extent upon the oxygen saturation of the arterial blood, especially with effort, and the total lung capacity.4. The ability to discriminate between these two diseases should improve our therapy and should enable us to arrest or even prevent a considerable proportion of them.