ABSTRACT— Ito cells (FSC) have been thought to be collagen-producing cells with regard to hepatic fibrosis. We have found that desmin, a structural protein of muscular intermediate filaments, is found in the cytoplasm of FSC, even in negative vitamin A-autofluorescence FSC, by using immunocytochemical techniques. In the present study, numbers of FSC produced by the administration of heterogeneic serum or carbon tetrachloride were detected in fibrous and non-fibrous areas of hepatic lobules by using a morphometrical analyser. After 8 weeks of intraperitoneal injections of heterogeneic serum into rats, FSC in fibrous septa increased in number and the increase continued to 12 weeks – although the numbers of FSC in non-fibrous areas and in controls given homologous serum did not change during the experiment. In the case of rats administered CCl4 once, FSC in fibrous areas increased in numbers after 48 h through 72 h, although the number of FSC in non-fibrous areas and in controls did not change. The results, with an apparent increase in numbers of FSC in fibrous areas and no change in non-fibrous areas, showed the possibility of hyperplasia due to cell division of FSC in the new fibroplastic areas.