In a 67 day old female kitten the morphological differentiation of the hepatic parenchyma was examined with the EM. Despite the advanced ultrastructural differentiation of the hepatocyte, the usual location of the Golgi complex to the apical cytoplasm around the bile canaliculus was not yet established. Numerous mitochondria are mingled with round microbodies characterized by a marginal plate and a crystalloid core. Tubular cisternae of the smooth endoplasmic reticulum occur only around the microbodies and lack within the accumulation of glycogen .alpha.-particles. The sinusoidal lining was fully differentiated and is composed of the cytoplasmic processes and the sieve plates whose fenestrae average 1300 .ANG. in diameter. Kupffer cell shows an active phagocytosis to blood cells. The fuzzy coat is unsatisfactorily preserved. The cytoplasm occasionally shows short segments of a worm-like body. The fat-storing cell (FSC) contains a small amount of lipid droplets which mostly appear within the dense accumulation of glycogen .beta.-particles. Also empty FSC devoid of lipid droplets mostly possess glycogen accumulations. The glycogen accumulations enclosing lipid droplets are closely juxtaposed by cisternae of the RER [rough endoplasmic reticulum] and mitochondria, suggesting the possible involvement of these organelles and glycogen in the lipid synthesis in the FSC. In most FSC, abundant cisternae of the RER are dilated and filled up with a finely flocculent material, suggesting an active production of collagen precursor. The FSC possess abundant microfilaments and microtubules. A single cilium is issued into the Disse''s space from one of the paired centrioles located in the Golgi area. The Disse''s space of the kitten contains, besides FSC, plasma cells and macrophages. The latter agree in ultrastructure with the Kupffer cells and are presumably transformed into them by being incorporated in the endothelial lining of the sinusoid.