In 34 elderly male and female patients undergoing upper abdominal surgery under general anaesthesia we investigated duration and degree of postoperative hypoxaemia. In this study only patients with no signs and symptoms of pulmonary or cardiac diseases, verified by normal lung function--vital capacity and FEV1, X-ray and electrocardiographic findings were considered. Postoperative development was free of complications and temperature rises in all cases. The investigations showed occurrence of arterial hypoxaemia during the postoperative period with values near the lower limit where the organism must fall back on cardio-circulatory reserve mechanisms in order to avoid general hypoxydosis. Regarding the restricted pulmonary and cardiac capacity for adaptation and compensation in geriatric patients, we recommend to prolong the practice of O2-application for two or three hours over a period of 24 to 48 hours, especially in patients with postoperative complications such as prolonged gastric atony, temperature, haemorrhage or cardiac and coronary insufficiency. This prolonged application of oxygen by mask or nasal tube should go parallel to other physiotherapeutic measures.