The carbohydrate metabolism in the carcinogenesis of DAB fed rat hepatoma was investigated by studying the G-6-Pase and Glucokinase activities to analyse the marked increase of glycolysis and decrease of respiration in the cancer tissue. And same time, these enzymes activities were measured in embrionic, new born, and regeneratig rat liver, which showed rapid growth and cell division, to study whether there was biochemical specificity in hepatoma. The liver homogenate G-6-Pase activity decreased progressively along with DAB feeding and was almost absent in the hepatoma tissue, while the glucokinase activity increased gradually and about 4 times of normal activity in cancer tissue. On the other hand, there was no change of glucokinase activity in the embrionic, new born, regenerating, or normal rat liver. And the G-6-Pase activity was almost absent in the embrionic rat liver and showed rapid increase after birth to maximum in 12th day born rat liver. From these results, both enzymes have important significance in the elevated glycolysis in cancer, although only G-6-Pase seems rate limiting factor in the physiologically elevated glycolysis state of the liver. So difinite difference was recognized between hepatoma and these tissues biochemically. The serum G-6-Pase activities in the carcinogenesis of DAB fed rat showed no significant change from normal rat. For clinical application, the serum G-6-Pase activities of various patients were also measured. Patients with hepatic disturbance especially acute hepatitis or active hepatitis demonstrated significant elevation of the G-6-Pase activity, while no other patient did not. So the measurement of serum G-6-Pase activity is very useful in clinical aspect.