Six well-trained subjects cycled (50% V̇O2max) for 180 min on two separate occasions. After 120 min, the subjects ingested 400 ml of either a 139 mM or a 589 mM glucose solution, then continued to cycle for another 60 min. Glucose-U-14C (1.85 × 103 kBq) was added to each drink. Venous blood samples were assayed for lactic acid, FFA, glucose, and glucose-14C activity. Expired 14CO2, urine-14C, and sweat 14C activity were also determined. By the end of exercise, the accumulated 14C recovered as 14CO2 was less than 10% of the dose. 14C activity in sweat and urine could account for less than 2% of the total ingested. Though little of the labeled glucose present in these drinks was used oxidatively, the 589 mM solution provided blood glucose in significantly greater amounts than did the less concentrated solution. Most of the ingested glucose seemed to remain in compartments within an unoxidized glucose pool.