A comparison was made between the pain-relieving effect of placebo-transcutaneous electrical nerve stimulation (TENS), high frequency TENS, and epidural analgesia with dilute local anesthetics in 15 patients with open knee surgery. Assessment of pain was compared with the patients' ability to contract their quadriceps muscle; the ability was measured with integrated EMG (IEMG) before and after the different treatments. The results showed that placebo-TENS had no significant effect on either pain perception or on IEMG. High frequency TENS given for 15 min to 20 min decreased pain perception by 50% at rest and by 11% after quadriceps contraction. High frequency TENS increased muscle contraction ability by 305%, compared with the initial contraction before treatment. Epidural injection of a dilute local anesthetic decreased pain perception by 90% at rest and by 67% after contraction, and increased muscle contraction ability by 1,846%. TENS undoubtedly has a place in the postoperative pain treatment, although its effect is not as strong as that of epidural analgesia with local anesthetics. TENS, however, is easy to administer, lacks side effects, and can be administered by the patients themselves.