Abstract: Chains of lumbar sympathetic ganglia, excised from 15-day-old chicken embryos, were incubated for 4 h at 36°C in a bicarbonate-buffered physiological salt solution containing 5.5 mM glucose and equilibrated with 5% CO2–95% O2. [U-14C]Glucose and [U-14C]lactate were used as tracers to measure the products of glucose and lactate metabolism, respectively, including CO2, lactate, and constituents of the tissue. When 5 mM lactate was added to bathing solution containing 5.5 mM glucose, lactate carbon displaced 50–70% of the glucose carbon otherwise used for CO2 production and provided about three times as much carbon for CO2 as did glucose. The lactate addition increased the total carbon incorporated into CO2 and into constituents of the tissue above those observed with glucose alone and also increased the lactate released to the bathing solution from [U-14C]-glucose. The latter increase was evidently due to an interference with reuptake of the lactate released from the ganglion cells, not to an increase in the cellular release itself. When the volume of bathing solution was increased 10-fold relative to that of the tissue, the average output of CO2 from [U-14C]glucose during a 4-h incubation was decreased by 50% when 5 mM lactate was present but was not affected significantly in the absence of added lactate. It is concluded that the effect of changing volume in the presence of lactate was due to the effects of lactate on glucose metabolism described above and resulted from a lower average lactate concentration in the smaller volume than in the larger one, due to metabolic depletion of the added lactate. Consumable substrates other than lactate, such as glutamine and certain amino acids, also affected glucose metabolism.