There have been many studies on the localization by immunocytochemistry of cytoskeletal proteins in cells cultured in vitro. However, the distribution of cytoskeleton in cells in situ has yet to be elucidated. In the present study we developed an immunohistochemical method for visualizing tubulin and actin in rat hepatocytes in situ, using a perfusion extraction-fixation procedure, in which the liver was perfused through the portal vein with a nonionic detergent to make the plasma membranes permeable to soluble substances, followed by a fixative to preserve cytoskeletal structure. Using the immunogold and peroxidase-antiperoxidase (PAP) staining procedures, we found that in hepatocytes in situ, tubulin was localized in cytoplasmic filamentous networks and in spindle fibers, as in hepatocytes and other cells in vitro. On the other hand, the distribution of actin in hepatocytes in situ was considerably different from that in well-spread hepatocytes and other cells cultured in vitro. In hepatocytes in situ, actin did not form any stress fibers, but was distributed preferentially under the plasma membrane, especially around the bile canaliculi. The perfusion extraction-fixation procedure could be adapted to visualize cytoskeleton in other tissues.