Forty-six patients with malignant tumours involving the orifices of the lobar bronchi were treated by lobectomy with sleeve resection of the bronchus. The results indicate that this procedure has many advantages when compared with pneumonectomy, which is the commonly practised alternative method of treatment. An immediate mortality rate following operation of 2·2% and a five-year survival rate of 35% are recorded. Simple lung function tests taken before and after surgery in a small unselected group showed that operation caused little physiological impairment.