A bipolar electrode has been designed to assess the possibility of locating accurately the electrode tip position within a nerve pathway prior to its thermal coagulation without having recourse to a wake-up procedure. By electrically stimulating each of the peripheral divisions of the trigeminal nerve and recording the evoked activity pre-ganglionically from the electrode, using an averaging computer, a clear triphasic response is recorded. The amplitude of this wave is largest when the electrode is within the stimulated division, thereby confirming electrically the anatomical location. By incorporating a thermocouple in the tip of the electrode a precisely controlled thermocoagulation can then be achieved using a radiofrequency generator. A preliminary series of 12 patients with trigeminal neuralgia requiring operative treatment were assessed in this study. In eight cases a clear response was obtained, in two the signal-to-noise ratio was too small, in one stimulus artefact obscured the response and in one a blood vessel was hit.