The lingual nerves from ten mice were examined so that normal axonal populations could be determined. After perfusion fixation, they were removed and processed, and sections were taken from nerves for transmission electron microscopy. The fiber-diameter spectrum of unmyelinated fibers for the mouse lingual nerve is characterized by a unimodal curve with the more pronounced peak in the medium-diameter fiber range (0.28 micron). The spectrum from the myelinated fibers also shows a population of axons of the lingual nerve (0.22-3.2 microns) that reflects different functional specializations. These data establish some baseline values for morphological evaluation of the effects of experimental lingual nerve damage.