According to a current theory about the pathogenesis of Bell's palsy, the motorfibers of the facial nerve are affected by a viral neuropathy, transmitted to the facial nerve via the axons of the chorda tympani nerve. We have used horseradish peroxidase (HRP) to test to what extent and under what conditions uptake and transport of macromolecules can take place from the tongue. When HRP was applied directly onto the mucosa, no labeling was observed. However, when applied to localized superficial lesions of the epithelium or injected into the tongue, HRP is transported retrogradely to the geniculate and trigeminal ganglia, superior salivatory and hypoglossal nuclei. Injection of HRP resulted in many more labeled cells as well as fiber labeling in the peripheral nerves, in the solitary and spinal trigeminal nuclei. The findings show that even after a minor superficial lesion in the tongue, exogenous macromolecules are taken up and transported to the intratemporal portion of the facial nerve as well as other cranial nerves. These findings are compatible with the theory that Bell's palsy is a neuropathy caused by neurotropic viruses spread via the chorda tympani.