Histological changes of liver biopsy specimens were compared with functioning liver cell mass estimated by an index, ICG capacity, and with plasma levels of various proteins, in 85 patients with liver diseases. IGC capacity was inversely proportional to the degrees of liver cell degeneration and lymphocyte infiltration in the portal tracts and parenchyma, in contrast to plasma disappearance rate of ICG (K), which was inversely proportional to the degrees of portal tract fibrosis and bridge formation. Among the plasma proteins synthesized in the liver, the plasma levels of prealbumin, and alpha1-acid glycoprotein showed the tendencies to decrease with the increase in the degrees of liver cell degeneration. The levels of ceruloplasmin, haptoglobin beta1A/C and transferrin were proportional to the degree of the degeneration. Plasma albumin had no correlation to any histological change. The plasma levels of gamma-globulin and IgG were both proportional to the degrees of portal tract fibrosis and bridge formation. IgM also paralleled to the degree of the fibrosis. The level of IgA was inversely proportional to the degree of liver cell swelling. It was concluded that quantitative estimations of some histological changes in the liver are valuable for the estimations of liver function and the grade of the diseases of the liver.