PURPOSE: This study was performed to evaluate the pre-emptive analgesic effects of a small dose of intravenous ketamine on postoperative pain in patients undergoing a hysterectomy. METHOD: Sixty patients undergoing a hystrectomy under general anesthesia were randomly allocated to 2 groups. The experimental group(30 patients) received 0.3mg/kg of ketamine after induction of anesthesia, approximately 5 min prior to surgery, but the control group(30 patients)did not receive ketamine. Data was collected in a double-blind manner from April 1st, to October 30th, 2004. Postoperatively, the patients used a patient-controlled analgesia(PCA) pump. Blood pressure, pulse rate, pain, anxiety, count of times pressing the PCA button, administeration of additional analgesics and side effects of ketamine were measured at 1 hour, 3 hours, 6 hours and 24 hours after the operation. RESULT: There were no statistical differences in blood pressure, pulse rate, pain and anxiety between the experimental and control groups. There were statistical differences in blood pressure, pulse rate, pain and anxiety during the 24 hours postoperatively. In the experimental group, the number of times pressing the PCA button and administering additional analgesic drugs were significantly lower than those of the control group. CONCLUSION: A 0.3 mg/kg dose of ketamine given at approximately 5 min before surgery resulted in decreasing the number of times pressing the PCA and the administration of additional analgesics.