In this study we aimed to investigate clinically whether morphine acts on the peripheral nervous system directly. Twenty adult patients, who were scheduled for upper extremity surgery under tourniquet, had intravenous regional anesthesia. They were divided into true groups: one group was given 30 ml of 1% prilocaine plus 10 mi of 0.9% sodium chloride CP group) and the other group was given 30 mi of 1% prilocaine plus 6 mg morphine sulfate in 10 ml of 0.9% sodium chloride P/M group). The onset of analgesia and anesthesia and recovery from anesthesia and analgesia were investigated in both groups. In the P/M group, the onset of analgesia and anesthesia was statistically faster and the recovery from anesthesia and analgesia was statistically slower than in the P group (P<0.05). We conclude that morphine is clinically effective in the peripheral nervous system at this dosage range.