BACKGROUND: Postoperative pain is the principal acute pain and many trials have been done for it. The preemptive analgesic method is one of the trials and nonsteroidal antiinflammatory drugs (NSAIDs) have been under study to reduce the side effects of opioids and to gain some other advantages, and many positive results have been reported. The author therefore planned this study to evaluate whether or not NSAIDs could have a preemptive effect, to observe any difference in effect with increasing dose, and to identify any advantage to patients under preemptive analgesia. METHODS: Seventy-five patients undergoing open cholecystectomy or choledochocystostomy were randomly allocated into three groups, group K0, K30 and K60. In group K0 (n = 25), patients were given no medication before operation. In groups K30 and K60, patients were given ketorolac 30 mg and 60 mg by intravenous route at 15 minutes before operation respectively. After operation, one observer who didn't know which group the patients were allocated to recorded patients' pain score (visual analogus scale; VAS and Prince-Henry score; PHS), side effects and satisfactory score at postpoperative 0, 1, 6, 12, 24 and 48 hours. For VAS > 50 or PHS > 3, morphine 2.5 mg was given by intravenous route and pain score was reestimated after 10 minutes and this was repeated until VAS < 50 and PHS < 3. RESULTS: In group K60, VAS, PHS and dose of morphine were lower than in other groups (p < 0.05). Satisfaction score was higher in group K60 and the nurse's satisfaction score was higher than the patient's in group K0 and K30 (p < 0.05). There was no significant difference in hospital days between groups. Side effects were negligible. CONCLUSIONS: Preoperative intravenous administration of ketorolac 60 mg in open cholecystectomy or choledochocystostomy could have a preemptive analgesic effect and give more satisfaction to patients. In the immediate postoperative period, pain status may be highest, so more attention and evaluation will be needed by pain management staffs for the proper management of acute pain.