BACKGROUND: The purpose of this study is to examine the effect of intravenous ketorolac administration before surgical stimulation for postoperative pain control. METHODS: Forty four patients scheduled for total hip replacement were randomly assigned to one of three groups of prospectively designed study. Group 1 (n=14) received intravenous saline (placebo) and Group 2 (n=15) received intravenous ketorolac (30 mg) at one hour after skin incision and Group 3 (n=15) received intravenous ketorolac (30 mg) before induction. Postoperative pain relief was provided with intravenous morphine from PCA system. Postoperative visual analogue pain score (VAS), analgesic requirement and side effects were evaluated and compared between groups for postoperative two days. RESULTS: VAS at rest were significantly less in Group 2,3 than in Group 1 at 3 hours after surgery (p<0.05) and significantly less in group 3 than in group 1 at 6 and 9 hours after surgery (p<0.05). VAS on movement were significantly less in group 3 than group 1 at 1 hour and significantly less in group 2,3 than group 1 at 3 and 6 hours after surgery (p<0.05). Patient controlled morphine consumption in group 1 was significantly higher than in group 2,3 for 12 hours after surgery. After administration of intravenous ketorolac any side effect did not occur. CONCLUSIONS: Administration of intravenous ketorolac before skin incision as a pre-emptive analgesia has better analgesia than those of 1 hour after skin incision and no administration of ketorolac.