Addis Ababa is situated at an altitude of approximately 8500 ft and has a barometric pressure of close to 570 mmHg. Arterial blood gas values during the administration of anaesthesia with spontaneous ventilation have not been extensively studied. During the period January to July 1993, oxygen saturation was determined in 46 unpremedicated patients prior to minor surgery. Following this, patients received diazepam 0.1-0.2 mg/kg and ketamine 2 mg/kg during which a clear airway was maintained and peripheral oximetry was monitored continuously. The SpO2 was recorded for each patient at one minute intervals until 5 minutes and thence at 7, 10 and 15 minutes. The average SpO2 decreased below 90% at 2, 3 and 4 minutes and of the 46 patients, 8 (17.3%) required additional oxygen when their saturation fell below 80%. It is concluded that airway management and supplemental oxygen should be available when using this technique.