Eleven patients with peripheral bronchial carcinoma had computerised tomographic (CT) scans before operation. The resected specimens from six of these patients showed mild centri-acinar emphysema. Preoperatively the two groups had not differed significantly in spirometric findings or lung volumes. The frequency distribution curves of EMI numbers within the lung fields of patients who proved to have centri-acinar emphysema differed significantly from those of the group who did not, there being more pixels in the EMI range -450 to -500 in the emphysematous group (p less than 0.001). Detailed assessment of lung density by CT scanning may be useful in the diagnosis of emphysema in life.