Effects of cianidanol on chronic liver injury induced by prolonged administration of carbon tetrachloride (CCl4) and on liver regeneration after partial hepatectomy of normal liver and CCl4 chronically injured liver were investigated by the measurement of plasma and liver biochemical parameters. Cianidanol increased the total plasma protein and 14C-Leu incorporation into plasma protein, while it reduced the contents of liver cholesterol and triglycerides. In rats with chronically injured liver or regenerating liver after partial hepatectomy of chronically injured liver, cianidanol improved the retention rate of BSP and the content of liver sugar. In rats with chronically injured liver, plasma GPT and GOT activities were reduced with the administration of cianidanol. Cianidanol had no effect on the regeneration rate after partial hepatectomy of normal liver, but it increased the regeneration rate after partial hepatectomy of chronically injured liver. These results suggest that cianidanol has the effect of improving the function of liver cells damaged by CCl4 treatment and of promoting the recovery of cell function to a normal level.