The osteoblast and osteocyte processes are filled with densely packed filaments, most of which have been previously shown to be actin microfilaments. However, the appearance of 10 nm diameter filaments in some cell processes and the fact that the intermediate filament vimentin has been identified in many cells of mesenchymal origin raised the possibility that some of these filaments might be vimentin. This study was performed to clarify the expression of the intermediate filament vimentin in cell bodies and processes of rat bone cells by immunohistochemistry and immunogold electron microscopy. Immunohistochemical staining showed that vimentin was expressed in cell bodies and processes of osteoblasts and osteocytes. The reactivities of osteocytes and osteoblasts were found in newly formed bone cortex, and the reactivity of osteocytes near bone marrow was stronger than its outer cortex in normal compact bone. Immunogold electron-microscopic study revealed that gold particle was identified clearly in relation to filaments within the cytoplasm of osteoblast and osteocyte cell body, throughout the entire length of the cell processes osteoblasts and osteocytes, and in close relationship to the intercellular gap junctions. Gold particles were present within the cell processes both close to the cell bodies and within the canaliculi well away from them. These results indicate that intermediate filament vimentin is distributed in cell bodies and processes of osteoblasts and osteocytes in rat bone.