A method of in situ perfusion of rat liver via the portal vein is described, by which osmiumtetroxide fixative can be introduced rapidly and uniformly to all parts of the tissue. Previous perfusion with balanced physiological saline solution, under the conditions described, of itself causes minimal change in the liver cell and liver architecture. Perfusion with a chelating agent causes no further detectable alteration within the liver cell but results in separation of the cells, even to the extent of producing a free cell suspension. The separation of cells is not accompanied by any recognizable damage to the plasma membrane but there is a striking tendency to pseudopod formation on the newly exposed surface. These findings provide direct evidence to support the classical concept of the importance of calcium to the adhesiveness of the plasma membrane in the tissues of the adult rat.