To compare the efficacy and side effects of midazolam and ketamine administered nasally for pediatric premedication. In this double blind trial 60 children scheduled for elective surgery were randomly assigned to two groups to receive 0.25 mg.kg or 5 mg.kg nasal ketamine. We measured level of acceptance of medication, sedation, hemodynamic variables, reaction to separation from parents, side effects and time until recovery from anesthesia. The two groups were homogeneous. Acceptance of medication was good or adequate in all patients. The level of sedation was significant in both groups 10 min after premedication. Systolic arterial pressure was higher in the ketamine group 20 min after administration of the drug and upon arrival in the operating theater. Reaction to separation from parents was good in all groups. Secretions were higher in the ketamine group and hallucinations were experienced by three patients in the ketamine group and by two in the midazolam group. We found no difference in time until spontaneous eye opening after surgery. No complications were observed. The nasal route is adequately accepted by children. Both drugs are effective by this route and sedation is rapid. Time until postanesthetic recovery is similar with both drugs. The doses used have wide safety margins.