A study was designed to evaluate the diagnostic usefulness as well as the mechanical determinants of the flow-volume contour in chronic obstructive pulmonary disease (COPD). Twenty patients with COPD of varying etiology were divided equally into two groups. Group 1 had an airway collapse pattern (described in the text) designated type 1, and group 2 had a more curvilinear obstructive pattern designated type 2. Pressure, volume, and flow relationships were examined. The results of our studies showed that a type 1 flow-volume contour in a patient with obstructive airways disease suggests a critical combination of central and peripheral airway collapse at high lung volumes with loss of elastic recoil. However, not all patients with loss of recoil will exhibit this contour. Persistence of type 1 contour suggests that there is a component of airway instability which may be irreversible.