Ventilation, pulmonary gas exchanges and oxygen transport were studied in a group of treated and untreated hypertensive elderly patients, before, during and after nitrous oxide-halothane anaesthesia with spontaneous ventilation. During anaesthesia minute and alveolar ventilation were depressed (— 30 per cent) out of proportion to the decrease in oxygen uptake (-18 per cent) and carbon dioxide production (— 19 per cent), and moderate hypercapnia ensued (mean Paoo3 50.3 mm Hg). All these variables returned to the pre-anaesthetic levels within 1 hour of terminating anaesthesia. VD/VT was increased following induction of anaesthesia as a result of decreased tidal volumes (— 47 per cent), but did not change progressively during the course of anaesthesia. Total deadspace (VD) was reduced by an average of 44 ml as a result of intubation. Based on measurements of arterial Poa and the alveolar-arterial Poj difference, mean pulmonary venous admixture was 10.4 per cent before anaesthesia, 10.9 per cent during anaesthesia but before surgery, 13.1 per cent after surgery, and 15.6 per cent 1 hour after the termination of anaesthesia. Although the average postoperative arterial Poa was slightly lower ( - 7.4 rnm Hg) than before anaesthesia, the difference was due to many factors, and no evidence of a deterioration in the over-all pulmonary gas exchange could be found. The concept of “airway closure” in the supine elderly subject as a cause for the increased pulmonary venous admixture at rest is discussed. Impairment of pulmonary function during anaesthesia in hypertensive elderly patients causes less concern than the severe changes in cardiovascular function