Phosphorylase activities and glycogen levels were determined in transplantable hepatomas in wistar rats, in transplantable mammary carcinomas in C₅₇B1 mice, in the livers of these tumor-bearing animals, and in the livers of control animals. In one series of experiments the animals were deprived of food for twenty-four hours. In a second series of experiments the tissues were analyzed two hours after the intraperitoneal injection of glucose into the 24-hour fasted animals. Phosphorylase and

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... gen were found to be very low in both tumors tested. The injection of glucose into the fasted animals resulted in marked changes in phosphorylase and glycogen in the normal liver but relatively little change in the tumor enzyme activity or in the tumor glycogen level. Evidence was obtained of an impairment in the glycogenetic function of the liver in the tumor-bearing animal. The relative amounts of the active and inactive forms of phosphorylase present in these various tissues were also ascertained by means of the co-factor adenylic acid. Purines and pyrimidines, other than adenylic acid, were found to have no activating or inhibiting effect on phosphorylase activity in normal liver, tumor-bearing liver and tumor from normal and tumor-bearing wistar rats and C₅₇B1 mice. Cellular fractionation indicated phosphorylase activity to be present in both the cytoplasmic and particulate fractions, in normal liver, tumor-bearing liver and tumor from normal and tumor-bearing wistar rats and C₅₇B1 mice.