In order to study the effect of spinal morphine on the tourniquet pain, 40 patients scheduled for orthopedic surgery on the lower extremity under spinal anesthesia were allocated randomly to two groups. In the experimental group, 20 patients received hyperbaric T-cain 10 mg and morphine 0.3 mg (0. 15 ml). In the control group, 20 patients received T-cain 10 mg and saline 0.15 ml. The levels of analgesia and motor block were similar in both groups. During surgery, patients in both groups did not complain of tourniquet pain, whereas one patient in the control group required general anesthesia for surgical pain although the sensory block extended to T(7). In the recovery room, when the sensory block had regressed to the Tdermatomal level, the pain response was checked on the contralateral unoperated thigh in a 60 min tourniquet pressure experiment (350 mmHg for 20 min, 0 mmHg for 20 min, 350 mmHg for 20 min). Seventeen patients in the experimental group experimenced no pain in this test, compared with four patients in the control group. From this study, it is suggested that intrathecal morphine prevents tourniquet pain and it may have some inhibitory effect on tourniquet pain transmission at the spinal cord level.