Segments of epididymal fat-pad tissue of rats were incubated with glucose labeled uniformly with 14C and in carbons 1 and 6 and with tritium in positions 3, 5, and 6. The effect of phenazine methosulfate (PMS) on incorporation of glucose carbon and tritium into metabolic products and on the formation and utilization of cytoplasmic and mitochondrial reducing equivalents was determined. PMS concentrations below 5 μ m have little effect on glucose metabolism. PMS between 5 and 100 μ m stimulates the uptake and oxidation of glucose but is without effect on its incorporation into fatty acids and glycerol. Higher concentrations of PMS inhibit glucose oxidation and lipogenesis. The lactate-pyruvate ratio in tissue incubated with glucose ranged from 3 to 10. With PMS the ratio was decreased to less than 0.5. At a PMS concentration of 50 μ m, glucose uptake was increased in tissue of fed rats by 30–50% and CO 2 production by 100–200%, The contribution of the pentose cycle to glucose metabolism increased from 15–20% to 40–50%, and oxidation via the Krebs cycle increased by 50–300%. In tissue of starved-refed rats with a very high rate of lipogenesis, the stimulation of the pentose cycle and Krebs cycle oxidation was less pronounced. A balance of reducing equivalents was calculated. In the absence of PMS the formation of cytoplasmic reducing equivalents is equal or in a small excess over that needed for lipogenesis and lactate production. In the presence of PMS a large excess is generated. The generation and utilization of ATP was calculated. Without PMS, ATP generation is in excess over that needed for known biosynthetic requirements. The excess is of the order of 20 μmoles/gram/hour for tissue of fed rats, and in tissue of fasted-refed rats, of the order of 40–50 μmoles/gram/hour. PMS increases oxidation via the Krebs cycle in tissue of normal rats but it is likely that the excess oxidation is not coupled to phosphorylation. When tissue was incubated with [5-T] glucose virtually the sole product was labeled water. This label is useful in measuring glucose uptake or turnover in vivo and in vitro by determination of the yield of labeled water. We conclude that lipogenesis is not affected by an increase in cellular pyruvate concentration or the NAD +/NADH and NADP +/NADPH ratios in the cytoplasm, or by a large decrease in the concentration of free reduced pyridine nucleotides.