['To determine the difference in performance of two different auditory evoked potentials (AEP) monitors, the A-Line AEP (AAI) and the aepEX, and their indices, during general anesthesia.', 'Prospective study.', 'Operating room at a private hospital.', '40 ASA physical status I and II women, aged 30 to 70 years, scheduled for partial mastectomy.', 'Anesthesia was induced with propofol and fentanyl, and a Laryngeal Mask Airway (LMA) was inserted. Anesthesia was maintained with propofol, fentanyl, and nitrous oxide.', 'The AAI or the aepEX was continuously monitored and their performance was compared at the start of monitoring, at LMA insertion, after disturbance by electric cautery, and during anesthesia. Eighteen of 20 patients had low enough impedance to extract good electroencephalogram signals at the first electrode application with the A-Line AEP, and 14 of 20 patients, with the aepEX. The time to return to good signals after signal disturbance by electric cautery was 14 +/- 3 seconds (SD) with the AAI and 19 +/- 4 seconds (SD) with the aepEX (P = 0.035). Both AAI and aepEX decreased after anesthesia induction, with significantly lower values seen in AAI than the aepEX.'] Does comparison of the two different auditory evoked potentials index monitor in propofol-fentanyl-nitrous oxide anesthesia?