Patients with trigeminal neuralgia are usually investigated by elicitation of the orbicularis oculi reflex and trigeminal evoked potentials. These neurophysiological methods do not allow direct judgement of the trigeminal nerve. By transcranial magnetic stimulation, however, non-invasive investigation of the efferent part of the trigeminal nerve is possible. 10 patients (4 men, 6 women, aged from 43 to 73 years) with trigeminal neuralgia affecting the second or third division were examined. In all patients bilateral long-latency responses after stimulation of the tractus corticonuclearis and short-latency responses after stimulation of the proximal part of the trigeminal nerve were registered. 8 patients showed normal short- and long-latency responses, while in one other patient the long-latency responses were delayed on both sides. The remaining patient revealed a significant difference of amplitude compared to the contralateral long-latency response. This patient had a pontine lesion as shown by blink reflex and a pathological trigeminal evoked potential. In both these latter patients multiple sclerosis was diagnosed. Use of transcranial magnetic stimulation may thus prove helpful in the differential diagnosis of neurological disorders presenting with trigeminal neuralgia.