Background:There is evidence that opioid receptors are present in peripheral tissues. This finding led to the application of peripheral opioids. The aim of this study was to evaluate the effectiveness of pre-incisional subcutaneous infiltration of morphine on post operative pain intensity in patients were candidate for upper abdominal surgeries.Methods:70 patients undergoing upper abdominal surgery entered into this prospective double blind study and divided into two equal groups. After induction of general anesthesia, they received a subcutaneous infiltration of morphine (10 ml, 0.1 mg/kg) or saline (10 ml) at the site of surgery. The operation was started 15 minutes after local infiltration and hemodynamic variables and also post operative pain intensity were assessed to 24 hours after surgery. Post operative cumulative morphine requirement and the time of first analgesic administration were recorded. Data was analyzed statistically using t-test and chi square.Findings:Mean pain score was significantly lower in morphine group than saline group at 4 and 6 hours after operation. (4.97±1.82 vs. 5.97±1.80, p=0.012 and 4.30±20 vs. 5.20±1.90, p=0.04 respectively). Mean pulse rate and its changes were significantly lower in morphine group than saline group at 5, 10 and 15 minutes after induction of anesthesia (p < 0.05).Conclusion:This study could not show the efficacy of subcutaneous infiltration of morphine on reducing post operative pain intensity in patients undergoing upper abdominal surgery. The reduction of pain intensity at 4 and 6 hours after surgery may be due to systemic absorption and analgesic effects of morphine.Key words:Post operative pain, morphine, infiltration, upper abdominal surgery