Noninvasive trigeminal evoked potentials: normative data and application to neuralgia patients. A mild electric shock applied to the lower lip was used to elicit reliable evoked potentials from the trigeminal nerve in 20 normal young adults. The wave forms were morphologically similar to those observed with invasive procedures. No substantial differences for either the right or left side of stimulation, recording electrode, or subject sex were obtained for any of the individual potential amplitudes or latencies. The same procedures were applied to 10 patients who had been treated with retrogasserian glycerol injections for trigeminal neuralgia. Trigeminal evoked potentials were elicited in all patients, although the quality of the individual wave forms was more variable than that observed for the normal subjects. Comparison of the treated with the unaffected face side in the patients demonstrated significantly smaller N2-P2 amplitudes and longer N2 latencies for the affected face side. The results suggest that these procedures produce reliable evoked potential measures of trigeminal nerve function noninvasively which can provide an objective index of treatment efficacy. 