The number of conducting airways less than 2 mm in internal diameter was only slightly reduced in the lungs of 12 patients with pulmonary emphysema and diminished flow rates. There was a change in the distribution of the smallest remaining airways, with a deficit of airways 0.4 to 0.6 mm in diameter and an excess of airways smaller than this. The change in airway caliber and number was small in emphysematous lungs and increased airway resistance in emphysematous lungs is more likely related to loss of elastic recoil, central flow limitation and associated chronic bronchitis.