Transcranial magnetic stimulation is a new technique used to stimulate brain areas as well as peripheral nerves in healthy, waking persons. To date this technique has appeared safe. The aim of the present study was to assess the clinical application of this method in patients with Bell's palsy. Electromyographic responses were elicited by electrical and magnetic transcranial stimulation of the facial nerve in 26 patients affected by Bell's palsy. Electrical stimulation: stimuli of 0.1 ms duration, and up to 15 V, were delivered through surface electrodes set 2.5 cm apart over the facial nerve at the stylomastoid foramen. Magnetic stimulation: the coil was placed tangent to the parieto-occipital surface of the scalp. The stimulus intensity was then increased stepwise until a supramaximal response was obtained. Recording: the focal recording electrode was placed ipsilateral to the side stimulated over the superior orbicularis oculi; the reference electrode was placed over the nasal bone. The patients were tested with two neurophysiological determinations: the first 15-30 days from the onset of the palsy; the second 30-60 days after the first. A clinical follow-up was performed six months after the second determination. The results indicate that, contrary to traditional electroneurography, transcranial magnetic stimulation is not able to supply useful neurophysiological indications in patients with Bell's palsy. Although the absence of compound muscle action potential upon stimulation of the side with the lesion did demonstrate some impediment to conduction, it did not have any prognostic value since it was also present in patients who were clinically well at the time of the second check-up.