Objective    To establish a stereological method for the quantitative study on corpus callosum and the myelinated nerve fibers in its callosal frontal region.     Methods    The volume of corpus callosum and the volume of its frontal region were estimated using the Cavalieri’s principle. The tissue blocks were obtained from the frontal region of corpus callosum in an uniform random fashion. Isotropic

uniform and random (IUR) sections were ensured by using isector t

echnique. Sections with the thickness of 60 nm were cut from each epon block by using an ultramicrotome. From each section

4 fields of vision were randomly photographed using electron microscopy. The length density of the myelinated fibers in the frontal region of rat corpus callosum was estimated using an unbiased counting frame. The volume density of the fibers was estimated using point counting. The total length and total volume of the myelinated fibers in the region were estimated by multiplying the length density and volume density of these fibers by the volume of the frontal region

respectively.     Results    The volume of rat corpus callosum  was (70.67±5.64) mm

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and the volume of its frontal region was (15.29±1.62) mm

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. The total length of these myelinated fibers was (16.01±2.28) km

and their total volume was (9.11±0.44) mm

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. The total volume of the myelin sheaths in the frontal region of rat corpus callosum was (3.91±0.40) mm

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. The diameter of these myelinated fibers was (0.58±0.05) μm.     Conclusion    We describe a stereological method that can be used to quantitatively investigate the volume of corpus callosum and the myelinated nerve fibers in the frontal region of corpus callosum. The method will be as a useful tool for the future studies of the changes of corpus callosum in normal aging and in various neurodegenerative diseases.