Rat livers were fixed by perfusion with glutaraldehyde via the portal vein and postfixed with a mixture of osmium tetroxide and potassium ferricyanide. Subsurface cisterns and vesicles were demonstrated, and, from serial sections, it appears that these organelles are part of large, fenestrated cisterns situated parallel to and at a distance of 20-40 nm from the lateral plasma membrane. Some of the cisterns possessed ribosomes on the surface facing the interior of the cell and, at points, they were continuous with the endoplasmic reticulum. From the lateral cisterns, tubules approached the plasma membrane facing the space of Disse and the sinusoid. A network of tubules was found in the vicinity of the bile canaliculus; a part of it lay close to the canalicular plasma membrane. Serial sectioning revealed that this network was continuous with the lateral cisterns via the endoplasmic reticulum. This morphology resembles that of tubulo-cisternal endoplasmic reticulum of such transporting epithelia as the choroid plexus and the renal proximal tubules.