Nalbuphine hydrochloride is a new analgesic structurally related to naloxone, a widely used narotic antagonist, and oxymorphone, a potent narcotic analgesic. Multiple clinical trials have verified the efficacy of nalbuphine in the relief of moderate to severe pain. In general, nalbuphine appears equal to morphine in both medical and surgical use at the same dosage levels and route of administration, although nalbuphine has a slightly longer duration of action. The purpose of this study was to assess the efficacy and side effects of nalbuphine in preoperative medication. Morphine and normal saline as placebo were included for comparison purpose. Eighty four patients who were scheduled to have an elective operation were included in this randomized, double-blind study. The patients received 0.17mg/kg of nalbuphine, 0.12mg/kg of morphine or 1 ml of normal saline respectively. by intramuscular injection one hour before arriving at operation room. Sedation, level of anxiety, emesis, subjective rating on the effect of premedication and side effects were evaluated. The results were as follows: 1) The sedation score was significantly lower in nalbuphine group than placebo group. 2) The level of anxiety was significantly lower in nalbuphine and morphine group than placebo group. 3) The frequency of emesis was not significantly different among three groups. 4) In the subjective rating on the effect of premedication, nalbuphine group was significantly more favorable than placbo group. 5) The side effects such as headache and dizziness were observed, and there were no significant differences in the frequency among three groups. The results indicate that nalbuphine may be recommended as an dffective premedication agent in those situation where opiods are considered as premedication agents.