The purpose of this study was to elucidate the submicroscopic pathological findings; of the Kupffer's cell observed to be swollen and increased in number on light microscope. In order to accomplish this purpose a small piece of the biopsied spicimens was fixed in Palade's cold buffered osmium tetraoxide and embedded in methacrylate. The material comprised in this study was such cases as normal, diabetes mellitus, hepatoses, and chronic viral hepatitis. Further, in order to investigate the function of the Kupffer's cell the correlation with morphological findings such as phagocytosis and snbsequent disintegration was studied. Intravenonsly administration of S. F. O. was carried out in the rats injured by carbon tetrachloride injection in advance. The animals were killed 24 hours or one month after the treatment. The results are as follows: 1) Normal liver. Both cytoplasmic and nuclear menbranes of the Kupffer's cell were relatively even. The smooth and rough surfaced endoplasmic reticulum were relatively poor in the development. Mitochondria and Golgi apparatus remained small in size. 2) Diabetes mellius. The Kupffer's cell was provided with numerous smooth surfaced endoplasmic reticulum. Increased reticular fibers often were found in the space of Disse. The fat-storing cell (Ito) having large fat vacuoles (inclusious) was observes between the liver cells and the endothelial lining. This was clearly differenciated from the Kupffer's cell. 3) Chronic viral hepatitis. The swelling of the Kupffer's cell and the endothelial lining occluded the lumen of the sinusoid. Both cytoplasmic and nuclear menbranes had irregular surfaces. Numerous electron dense vacuoles and smooth surfaced endoplasmic reticulum were observed. These findings were thought to represent the state of hyperfunction. 4) The Kupffer's cell intoxicated by carbon tetrachloride and injected of S. F. O. showed increased number of mitochondria, both rough and smooth surfaced endoplasmic reticulum and vacuoles, in comparison with those of normal rat liver. Phagocytosed S. F. O, were found to locate as aggregates with single menbrane or as electron deuce particles in the vacuoles, in normal rat, besides in the intoxicated cases, S. F. O. were scattered in to the hepatic cellular cytoplasm. The latter was observed to be in the state of hyperfunction in phagocytosis. In the case of chronic carbon tetrachloride intoxication, iron aggregates remained in ferritin as long as one month while disappeared mostly in the case of normal rat liver.