The use of room air alone to ventilate patients who were anaesthetized with total intravenous anaesthesia, including morphine 2 mg.kg-1, was studied in ten patients. The were scheduled for gastrectomy for peptic ulcer or stomach carcinoma. The patient's minute-ventilation was measured the day previous to surgery; this, together with a frequency of 14 c.min-1, was used to preset the ventilator. Alveolar ventilation, end-expiratory CO2, arterial blood gases and acid-base balance were monitored throughout the procedure. The blood oxygen level was found to remain similar to the reference value; there was a moderate hypocapnia, a low end-expiratory CO2 and minimal changes in acid-base balance. No pulmonary complication was encountered in the postoperative course. These results showed that room air could be used in unusual circumstances for healthy patients for whom a total intravenous anaesthetic technique has been chosen.