Fibreoptic bronchoscopy was performed in 69 out of 73 consecutive patients with carcinoma of the lung, in four of whom a second synchronous bronchial carcinoma was found in the opposite lung. Three of these second tumours were radiographically occult. Another patient with a radiologically occult bronchial carcinoma in the right upper lobe bronchus had 16 years earlier undergone a left lower lobe resection because of a squamous cell carcinoma. These findings emphasize the importance of careful bronchoscopic examination of the whole bronchial tree before surgical treatment of the lung cancer.