Liver carcinogenesis induced by diethylnitrosamine (DEN) was studied in 19 male albino rats under electron microscope. The effects of DEN on hepatocytes included following basic abnomalities:1. The characteristic features of the nucleus are irregulat in shape, increase of interchromatin granules, and decrease of nucleolus-associated chromatin. The nucleoli are enlarged, irregular in shape and showing remarkable deformity of nucleolonema.2. The characteristic features of the cytoplasm are as follows. The mitochondria increase or decrease in number and size, they are irregular in shape with some variation in cristal pattern. Endoplasmic reticulum (ER) increases in the width of the lumina, detachment of some ribosomes from the membraneous component of rough endoplasmic reticulum (RER) and the appearance of concentric bodies of ER (RER concentric body or SER concentric body).3. The characteristic features of the cell membrane are the increase in the number of microvilli facing the Disses' space, the enlargement of bile canaliculi with increase or decrease in number of microvilli. Plasmalemma connecting between the adjacent hepatoma cells may be straight, wavelike or interdigitated.

This paper presents the results of an ultrustructural study of the hepatoma cell lines FSK 7901, FSK 7902 of long term cultures about 2 years more.The size of cell varies. Distribution of the cell is single or in epitheloid monolayer. Pseudopodial processes or microvilli cover the perimeter of certain hepatoma cells. In the monolayer, the microvilli exist where the neighboring plasmalemmae are in loose contact. When their contact is close, the neighboring plasmalemmae may be straight, wavelike or interdigitated. The nucleus and enlarged nucleoli are irregu- lar in shape. The deformity of nucleolonema is remarkable.Rough endoplasmic reticulum (RER) and mitochondria are much less in number in the cytoplasm, but the free ribosomes is very abundant. The shape of mitochondria and their cristae are irregular. The Golgi complex is often or less arranged around 10 in a group, situated near the nucleus. Typical coucentric body from RER or SER has not been observed. Annulate lamellae are easily found. A peculiar structure, primordial rough-surfaced endoplasmic reticulum (PRER) is seen.Juxta-nuclear acidophilic area consists of a group of Goigi complex or Golgi complex and mitochondria.