In a randomized cross-over study on sedation in outpatient oral surgery, intravenous and rectal administration of diazepam were compared. The mean dose for intravenous diazepam was 0.22 mg X kg-1 (range 0.15-0.38) and for rectal diazepam 0.58 mg X kg-1 (range 0.50-0.71). The determining factors for the patients' preference for sedation method, apprehension, effect produced by the sedative, recovery from sedation and the postoperative course were studied. The patients preferred the session in which they experienced stronger effect, regardless of the route of administration. Patient preference for sedation method did not differ when optimal dose regimens were used, and a preset dose of 10 mg rectal diazepam did not produce the desired effect. Apprehension was significantly higher prior to and during the first operation than the second operation, and all patients recovered from sedation within 2 1/2 hours after the administration.