Transbronchial needle aspiration has recently been adapted for use with the flexible bronchoscope. We studied 108 patients, who had a total of 110 aspirations performed, and diagnosed thoracic cancer in 70 cases. Transbronchial needle aspiration revealed malignant disease in 32 (46%) of these 70 patients. In 12 (17%) patients with cancer this technique provided the sole cytological or histological confirmation of the diagnosis. It gave a positive result in an additional 20 (29%) cases in which the diagnosis was also proved by conventional procedures, and it provided important staging information in these patients. In 20% of patients with cancer transbronchial needle aspiration precluded the need for further diagnostic surgery. There were no complications in this series. This is a safe, useful, and economical technique that can be used in diagnosing and staging patients with carcinoma of the lung.