Of 4,000 patients with bronchial carcinoma, the histology of the tumour was known in all but 5.8 per cent; nearly 48 per cent of tumours were squamous; 40 per cent were undifferentiated; 5 per cent were adenocarcinomata; in 17 patients the tumour was an alveolar cell carcinoma; in 56 patients submitted to exploratory thoracotomy the histology of the tumour was mixed. More than half the patients with adenocarcimoa and alveolar cell carcinoma were surgically managed. Mediastinal glandular metastases from squamous or undifferentiated carcinoma demonstrated after pulmonary resection, did not preclude long survival. Operative mortality after pneumonectomy was relatively highest in those with an adenocarcinoma. There was evidence at necropsy of distant spread in more than 80 per cent of patients who died in the early post-operative period after pneumonectomy. One in every 3 patients who died from metastases in the first 2 years after pneumonectomy died with cerebral metastases. Lobectomy in 65 per cent of patients was for squamous carcinoma, and was only slightly more common for undifferentiated carcinoma (18%) than for adenocarcinoma (15%). Long survival after lobectomy for squamous or undifferentiated carcinoma with glandular metastases was not uncommon. Bronchial carcinoma in patients who presented without symptoms and with an abnormal routine chest radiograph was most often squamous, peripheral in type, and small. In this group the rate of resectability and of long survival were high and operative mortality was small. A third of the patients with bronchial carcinoma, who denied ever having smoked, had squamous tumours. The incidence of adenocarcinoma in women, and those with hypertrophic pulmonary osteoarthropathy, was significantly higher. The incidence of resectability with long survival in a small group of patients with alveolar cell carcinoma was surprisingly high.