Several lung function tests are capable of detecting typical functional abnormalities in pulmonary emphysema, such as reduced elastic recoil of lung tissue, elevation of intrathoracic gas volumes, expiratory bronchial collapse or uneven patterns of ventilation. The measurement of elastic recoil by means of an esophageal catheter also seems to be a reliable technique for detecting early stages of emphysema, but its use for routine clinical investigations remains impracticable. The elevation of intrathoracic gas volumes determined by body plethysmography or helium dilution technique may sometimes be influenced by reversible bronchial obstructions or additional restrictive ventilatory defects. Expiratory collapse of the intrathoracic airways, however, proves to be a regular finding in advanced pulmonary emphysema. It results from decreased stability of the peripheral and central bronchial wall as well as from a shifting of bronchial and transmural pressure gradients to the peripheral airways. The occurrence of a pressure dependent expiratory stenosis can easily be demonstrated by the spirometric flow-volume curve during forced expiration, thus differentiating patients with asthma from those with chronic bronchitis and emphysema. The minimal program for detection and evaluation of emphysematous alterations of the lung by functional tests should consist in the measurement of intrathoracic gas volumes, recording of the forced expiratory volume and the analysis of the flow-volume curve.