We visualized the surface of ultra-thin sections of rat liver and kidney embedded in LR White resin using an atomic force microscope. The section surface always showed depressions corresponding to the embedded cells at the plasma membrane, at the basal lamina, at mitochondria, and chromatin blocks in the nucleus. The depth of the depression corresponding to the plasma membrane was about 6 nm in both hepatocytes and several types of kidney cells. At the basal lamina, mitochondria, and the chromatin blocks, sections showed deeper depressions of about 10-30 nm. In addition, cytoplasmic surfaces showed strong relief, 3-4 nm on average. The surfaces of the resin block left after ultrathin sectioning showed protrusions corresponding to cells, mitochondria, and the chromatin blocks. In marked contrast, the surface of epon sections was much smoother than that of LR White sections, without showing any marked depressions and relief except for the chromatin blocks of the nucleus. The relation of the surface morphology of the ultrathin sections to the efficiency of immunolabeling is discussed.