Fifty-one male rats (body weights:200—350gm) were raised with laboratory diet, 39 of them were injected once a week with CCl_4 (0.015cc/100gm body weight) in li- quid paraffin through the mesenteric veins and 12 rats without treatment as controls. Rats with 1,2,3,and 4 injections were killed 7 days afterwards.Pieces of liver tissue were taken from the left anterior lobe of the rats from both experimental and control groups.Paraffin sections were prepared from materials fixed in:(1)Susa or Stieve's for Heidenhain's Azan staining;(2)Regaud's for Bensley's acid fuchsin-methyl green staining of mitochondria;(3)cold Carnoy's for methyl green-pyronin staining of ribo- nucleic acid (RNA),with control sections extracted with 20% perchloric acid or 0.17 M NaCl at 56℃ for 2 hrs.;(4)Carnoy's for Yakovlev's ((?)) and Barrnett- Seligman's methods for protein-bound SH-group,with control sections blocked with 0.1M monoiodoacetic acid;(5)Formol-alcohol for Hotchkiss's periodic acid-Schiff's (PAS) reaction of glycogen,with control sections treated with salivary digestion;(6)cold ace- tone for alkaline phosphatase (ALP);and (7) 10% neutral formalin for frozen sections and Sudan Ⅲ testing for fats. After CCl_4-intoxication,during the development of cirrhosis,most of the parenchymal cells degenerated and finally became necrotic.Free fat droplets and hyperplastic fibrous tissues accumulated in the necrotic regions.The liver lobules thus were destroyed and blood sinuses were engorged with blood cells.Surviving cells showed compensative hyperplasia and were isolated into nodules by the developing fibrous tissues.Cirrhosis developed in all the rats treated with CCl_4. The parenchymal cells showed a progressive changes during the development of cirrhosis.There was an increase of fat droplets and a decrease of the number of mito- chondria in the cytoplasm.The mitochondria fragmented into granules or fused in a mass.There was a progressive decline in the content of RNA and glycogen,but an increase of the ALP activity.Those cells showing compensative hyperplasia enlarged in size,and their number of mitochondria,RNA and glycogen content progressively in- creased. Small-sized cells appeared in the necrotic regions among the fat droplets,necrotic cells and fibrous tissues.They decreased in number as the fibrous tissue developed. These cells contained mitochondria and showed positive reactions of PAS,RNA and ALP.Their origin was discussed and their relation to the formation of collagen fibers needs further investigation.