Essential differences are established between the activities in enzymes of monophosphohexoses' transformation in the Zajdela hepatoma and liver of tumour-bearing rats. So, a very low hexokinase activity is observed in the liver, the activity of phosphoglucomutase and glucose-6-phosphate being high. In hepatoma cells the activity of hexokinase is relatively high and that of phosphoglucomutase, glucose-6-phosphate phosphatase and dehydrogenases--glucose-6-phosphate and 6-phosphogluconate inhibiting the activity of phosphoglucomutase is considerably lower. Significant differences are also found in the ratios of the glucose, glucose-6-phosphate, fructose and fructose-6-phosphate concentrations, that evidences for changes in the regulatory mechanisms in the hepatoma cells.