To compare the clinical characteristics of two oral premedicants, midazolam and ketamine, 40 healthy children, one to six years of age, who were scheduled for ambulatory dental surgery, were assigned to receive either oral midazolam 0.5 mg.kg-1 or oral ketamine 5.0 mg.kg-1 in a double-blind, randomized study. Sedation and anxiolysis scores before induction, cooperation at induction of anaesthesia and recovery times and complications were assessed. We found that both drugs effectively sedated the children within 20 min of administration. Although sedated, 10% of the children in the midazolam group and 20% of those in the ketamine group became tearful on separation from their parents and 20% of those in the midazolam group and 35% of those in the ketamine group became tearful when the facemask was applied. No important side effects were attributable to either premedication. The time until the children were fit for discharge from the hospital after midazolam was approximately 20 min less than after ketamine. In conclusion, midazolam and ketamine offer similar clinical characteristics when used as oral premedications for children undergoing ambulatory surgery, although the time to discharge from hospital may be more rapid after midazolam than after ketamine.