SUMMARY:The purpose of this paper was to study the sensory myelinated and unmyelinated nerve fibers found in the subepithelial lamina propria of tongue mucosa of aging rats. It was used the silver impregnation, transmission electron microscopy methods and morphometric measurements. The results revealed that subepithelial nerve fiber bundles of the anterior, medium and posterior regions of tongue were arise from deep muscular layer of tongue. The nerve fiber bundles were verified inside of the connective tissue of lamina propria. These nerve fibers branched several times and into the connective tissue papillae they form a single or ramified sensory nerve endings. The fungiform and vallate papillae contain numerous nerve terminals. The fine structure demonstrated that in the axoplasm were noted the presence of neurofilaments, mitochondria and microtubules. Although the morphometric data of myelinated fibers showed that about 44% having larger diameter between 3 to 4 µm and the mean value was 4.5 µm. The largest diameter was 12 µm and the smaller was 1.4 um. The smallest diameter ranges from 1 to 3 µm, being that the mean value was 2.33 µm. Concerning to the thickness of myelin sheets were revealed the values ranging from 0.2 to 0.8 µm being that the 90% present the values around 0.5 µm. The unmyelinated fibers showed the largest diameter (62%) varying from 0.25 to 0.75 µm. The mean value was 0.6 µm being the maximum value was 3.17 µm and the minimum was 0.2 µm. The smallest diameter was obtained in 44% of unmyelinated fibers which the diameter ranges from 0.2 to 0.4 µm.Then maximum value obtained was 1 µm and the minimum was 0.12 µm.KEY WORDS: Nerve fiber; Myelinated fiber; Unmyelinated fiber; Tongue mucosa; Aging rat; TEM. * Department of Anatomy, Institute of Biomedical Sciences, University of São Paulo, Brasil. dfgrisolia@uol.com.br ** Department of Anatomy, University of Fukuoka School of Medicine, Japan.This paper was supported in part by CNPq Grant. 408For light microscopy, were used 3 animals. The tongue were removed and divided in three portions: anterior, medium and posterior, which were fixed in 10% formolin solution, during 20 days, at room temperature. Then, the tissues were cooled in liquid nitrogen and the sections of 40 to 50 µm were obtained in Kriostat Young. The tissues were treated for silver impregnation method, according to the technique reported by Winkelmann & Schmitt (1957) and Watanabe & Semprini (1985). The samples were mounted and examined by Zeiss photomicroscopy.For transmission electron microscopy, the small pieces of anterior, medium and posterior parts of tongue were fixed in modified Karnovsky solution, containing 2.5% glutaradehyde, 2% paraformaldehyde in 0.1 M sodium phosphate buffer at 4 ºC (pH 7.3), according to the technique reported by Watanabe & Yamada (1983). Then, the tissues were rinsed in phosphate buffer for 15 min, and postfixed in 1% buffered osmium tetroxide for 2 h at 4 ºC. The dehydration was done at room temperature with increasing series of ethanol, and they we...