To evaluate the influence of upper respiratory tract surgery on respiratory function, we used a pulse oximeter to measure the arterial oxygen saturation in 40 patients (ASA 1 or 2) during surgery under local anesthesia. The patients were divided into four groups: a control group of 10 patients who underwent surgery not involving the upper respiratory tract, and three upper respiratory tract surgery groups of 10 patients each underwent surgery on the nasal cavity alone (group 1), on the oral cavity alone (group 2), and on both the oral and nasal cavities (group 3). Groups 1 and 2 showed little desaturation compared to their baseline levels and the control group, while group 3 showed a mild desaturation even at the beginning of surgery and this gradually turned to a moderate or severe desaturation. This was due to both the extension of the surgical zone to the nasal and oral cavities and to ventilatory distress produced by massive bleeding and aspiration of secretions. Thus, the pulse oximeter is a useful monitor for upper respiratory tract surgery involving both general and local anesthesia. It allows the identification of hypoxia so that remedial therapy can be instituted.