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We investigated 15 patients with unilateral facial paralysis using gadolinium(Gd)-DTPA (diethylenetriamine pentaacetic acid) enhanced (magnetic resonance imaging (MRI). Eleven were idiopathic and 1 each was due to basal skill trauma, Lyme's disease, Foville's syndrome and herpes zoster oticus. Ten of 11 Bell's palsies showed a significant enhancement of the facial nerve on the paralysed side. In all cases enhancement was shown in the labyrinthine segment, in 9 in the meatal segment, in 8 in the mastoid segment and in 7 in the tympanic segment also. Follow-up Gd-enhanced MRI investigation was performed 3-11 months later in 8 patients. In 1 case with incomplete return of function after 3 months MRI enhancement was decreased. We could not find any correlation between the intensity of the Gd enhancement and the course, severity or outcome of Bell's palsy, or stapedius reflex audiometry. The mechanisms and aetiology of the Gd enhancement in Bell's palsy seem to be non-specific phenomena which are also found in post-traumatic facial lesions, for instance. Nevertheless, the ability to image the facial nerve in Bell's palsy provides a new means of examination in this disorder. In our opinion Gd-enhanced MRI is recommended in cases of recurrent or "atypical" Bell's palsy and in cases with total loss of electrical excitability, to exclude tumours. It is further suggested that MRI may provide valuable information concerning areas which may require surgical exploration or decompression.