Electrical and physiological stimulation in the periphery evokes potentials which can be recorded in the target region during stereotactic surgery. This procedure, combined with intracerebral stimulation, is commonly used as a method to verify the localization of the tip of the probe. We recorded evoked potentials following electrical stimulation of a peripheral nerve during stereotactic operations of patients with parkinsonian tremor and spasmodic torticollis, in order to qualify the functional modalities of the fiber system which might be interrupted by a lesion in the target area. Therefore, mixed nerves (median nerve at the wrist, ulnar and median nerve in the brachial sulcus) were stimulated with a bipolar surface electrode contralateral to the operated side. In contrast, skin nerves were stimulated by a loop electrode around the tips of fingers 2–5 on the same side. The evoked potentials recorded in the target region were generally biphasic with an initially positive deflection at a latency of about 14 ms following median nerve stimulation at the wirst. No significant potential was recorded when the skin afferents were stimulated. The recording sites were plotted by computer with reference to the third ventricle and transferred to the stereotactic atlas using special software.