Abstract 1. 1. Parenchymal cells isolated from the livers of 16-h-fasted rats have a very low ability to utilize glocuse. At 20 mM glucose, there is no net glucose consumption, no stimulation of respiration, and very low rates of glycolysis and glycogen synthesis. Cells from fed rats consume glucose more readily. 2. 2. Fructose is utilized very effectively by isolated liver cells from both fed and fasted rats. At 20 mM fructose, respiration is approximately doubled (i.e. there is no Crabtree effect), the rate of gluconeogenesis is high, glycogen accumulates and the glycolytic rate is 10 – 30 times higher than with glucose under aerobic as well as anaerobic conditions. 3. 3. Gluconeogenesis (formation of glucose + glycogen) from lactate, pyruvate or fructose is not subject to end-product inhibition by glucose at physiological concentrations (5 – 20 mM) in cells from fasted rats. However, glocose has a stimulatory and probably direct effect on glycogen synthesis, thereby directing a greater fraction of the gluconeogenic precursors into glycogen. Liver cells from 40-h-starved rats have largely lost the ability to synthetize glycogen. 4. 4. Glycogins (from fructose) is strongly inhibited by the end-product lactate under aerobic conditions. 5. 5. Lactate, but bit pyruvate, also slightly inhibits glycogen synthesis from high concentrations of fructose. Quinolinate, which blocks gluconeogenesis from lactate (but not from fructose) does not prevent lactate inhibition of glycogen synthesis, but since quinolinate alone stimulates glycogen synthesis the specificity of this inhibitor is doubtful. 6. 6. Under anaerobic conditions, glycolysins from fructose is strongly stimulated (classical Pasteur effect) whereas gluconeogenesis and glycogen synthesis are blocked. The end-product inhibition of glycolysis by lactate also largely disappears during anaerobis. Since previous experiments have shown that anoxia furthermore stimulates glycogenolysis and abolishes the glycogenolytic control function of glucose, the concept of “generalized Pasteur effect” introduced in order to emphasize the multiplicity of oxygen effects on liver cabohydrate metabolism.