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Transcutaneous electrical nerve stimulation (TENS) at either an acupoint or dermatome corresponding to the surgical incision produces comparable decreases in postoperative opioid requirements and opioid-related side effects. However, the effect of the frequency of the electrical stimulus on the postoperative analgesic response to TENS therapy has not been studied.One hundred women undergoing major gynecological procedures with a standardized general anesthetic technique were enrolled in the study. Patients were randomly assigned to four groups: group I, patient-controlled analgesia (PCA) plus sham TENS (no stimulation); group II, PCA plus low-frequency (2-Hz) TENS; group III, PCA plus high-frequency (100-Hz) TENS; group IV, PCA plus mixed-frequency (2- and 100-Hz) TENS. The PCA device was programmed to deliver 2–3 mg intravenous boluses of morphine with a lockout interval of 10 min. The TENS device was used every 2 h during the day. Standard 100-mm visual analog scales were used to assess pain, sedation, fatigue, and nausea at specific intervals after surgery.Mixed frequency (2 and 100 Hz) of stimulation decreased morphine requirements by 53% compared with the sham group; low (2-Hz) and high (100-Hz) frequencies produced 32% and 35% decreases, respectively. All three “active” TENS groups reduced the duration of PCA therapy, as well as the incidence of nausea, dizziness, and itching.TENS decreased postoperative opioid analgesic requirements and opioid-related side effects when utilized as an adjunct to PCA after lower abdominal surgery. Use of TENS at mixed (2- and 100-Hz) frequencies of stimulation produced a slightly greater opioid-sparing effect than either low (2-Hz) or high (100 Hz) frequencies alone.