Lactic acid formation from glycogen and glucose, a-glucan phosphorylase, glucoktnase, glucosephosphate isomerase, fructosediphosphate aldolase, glyceraldehydephosphate dehydrogenase, phosphoglyceratekinase, phosphopyruvate hydratase and pyruvate kinase are decreased in the liver of rats, which had been treated with propyl-thiouracil. Phosphoglucomutase, phosphofructokinase, phosphoglycero-mutase and lactic dehydrogenase are unchanged. Lactic acid formation from ribose-5-phosphate and the activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase are decreased, while transketolase is unchanged. Malic enzyme, malate dehydrogenase, oxaloacetate decarboxylase, glucose-6-phosphatase and UDPG-glycogen glucosyltransferase are decreased, whereas hexosediphosphatase is unchanged and UDPG pyrophosphorylase is increased. Glycogen is accumulated in the liver of treated rats. The incorporation of [C^*] pyruvate in glycogen is decreased.