Forty-eight percutaneous needle biopsies of the lung were performed on 40 patients, 17 with localized peripheral lung tumors and 23 with bilateral diffuse disease. A diagnosis was achieved in 32 (80 per cent) of the patients. The primary complications were pneumothorax (23 per cent) and hemorrhage (21 per cent). No deaths occurred. Prompt use of a chest tube eliminated pneumothorax as a danger. The hazard of pulmonary hemorrhage can be reduced by limiting the depth of the biopsy. Repeat biopsy is often helpful in diagnostic failures, especially in those patients with peripheral densities whose initial biopsies show only scar tissue or necrosis. It was concluded that percutaneous lung biopsy using a cutting needle is a rewarding and comparatively safe diagnostic procedure in patients with solid, peripheral lung lesions, but in patients with diffuse pulmonary disease there is less success in obtaining tissue and a significantly greater rate of complication. Of the other biopsy techniques, trephine lung biop...