A method of abrasive biopsy of the peripheral bronchial tree is described. Forty-nine patients with peripheral pulmonary lesions have been investigated, and at bronchoscopy brush biopsies have been performed. In 13 cases a firm diagnosis of bronchial carcinoma was made and in nine patients atypical cells were reported. Two of the latter were found on further investigation to have had no carcinoma and one showed squamous metaplasia only on surgical biopsy. In nine patients a false negative result was obtained. These results suggest that the routine use of brush biopsy during bronchoscopy performed in the investigation of peripheral pulmonary lesions helps to increase the accuracy of diagnosis.