Hepatocytes of precision-cut rat liver slices were studied by means of transmission electron microscopy after long-term incubation (24-48 h) in comparison with freshly prepared slices, indicating reversible and irreversible intracellular alterations of the cells. After 24 h incubation the morphological image in transversal sections of slices is characterised by a central zone of damaged and necrotic cells flanked by two to several superficial layers of viable cells. This is typical of a diffusion gradient of oxygen tension and nutrient content from the surface to the centre of the slices. In adapted cells on the surface of the slices we observed an organelle-free layer of fine granular material in the apical cytoplasm followed by parallel oriented stacks of rough endoplasmic reticulum near by. Mitochondria of essentially normal appearance in adapted cells did not contain flocculent densities, which were observed in damaged cells only. The cytoplasm of parenchymal cells consisted of defined areas of clear cytoplasmic material containing numerous branching tubular profiles of smooth endoplasmic reticulum, presumably in the regions with depleted glycogen aggregates. Subcellular signs of necrosis are destroyed mitochondria, dilated endoplasmic reticulum free of ribosomes and clumping of chromatin in the nucleus of hepatocytes. No appreciable differences of the cell organelles were observed between 24 and 48 h of incubation, but the incidence and intensity of signs of necrosis increased with the duration of incubation and the thickness of the slices. The process of these changes may reflect the phenomenon of cellular adaptation and of hypoxic cellular injury in the periphery and the centre of the slices, respectively.