Two different isozymes of lactate dehydrogenase, skeletal muscle type (LDH-M₄) and cardiac muscle type (LDH-H₄), were purified to a high degree from rat skeletal muscle. The distribution of each isozyme in rat liver was investigated by use of the peroxidase-labeled antibody method at light and electron microscopic levels. Using histochemical technique, the final reaction deposits were recognized in the cytoplasm, near the cell membrane facing both Disse's space and bile canaliculi, and in the mitochondria. By using the peroxidase-labeled antibody method, LDH-M₄ was demonstrated in an amorphous part of the cytoplasm of the parenchymal cells, which might correspond to the glycogen area. On the other hand, LDH-H₄ isozyme was localized in amorphous cytoplasm near the cell membrane facing both the bile canaliculi and Disse's space, and in the mitochondria of parenchymal cells.
In both histochemical and immunohistochemical studies, lactate dehydrogenase was recognized neither in the stellate cells of Kupffer nor in the endothelial cells of the sinusoid.