The use of ketamine in adults has been complicated by untoward hallucinatory emergence reactions. The addition of nitrous oxide and diazepam to subanesthetic doses of ketamine may be effective in decreasing these reactions. Adult patients were sedated for outpatient oral and maxillofacial surgery procedures using nitrous oxide, diazepam, and either fentanyl or ketamine. Postoperative questionnaires were used to evaluate hallucinatory reactions, amnesia, and patient acceptance. Comparison of the results of patients receiving ketamine and those receiving fentanyl revealed no statistical differences in hallucinatory reactions or patient acceptance. Amnesia was more complete in the ketamine than the fentanyl group.