This study investigated the levels of oxygen saturation and pulse rates of patients undergoing minor oral surgery under local analgesia, with (20 patients) or without (20 patients) intravenous sedation with midazolam. The results indicated that a statistically significant fall in arterial blood oxygenation of 1% to 2%, as measured by pulse oximetry, followed midazolam administration; however, this was physiologically insignificant. Both groups showed a similar postoperative small fall in oxygen saturation. Transient episodes (24 to 36 seconds) of physiologically significant mild hypoxia occurred during breath holding, but this condition was readily corrected by encouraging patients to breathe deeply. Midazolam had a small but significant calming effect on the higher preoperative pulse rates exhibited by anxious patients, but this effect was not sustained during the operating period. Both sedated and unsedated patients showed episodes of tachycardia that could have significance for patients with cardiac disease.