A diverse group of studies, which are equine exclusive, indicate that ribose administered to myocardial and skeletal muscle tissue stimulates ATP production and recovery. This study investigated the effects of ribose supplementation on blood and muscle metabolites and performance in Thoroughbred geldings performing a maximal treadmill standardised exercise test (SET). In Experiment 1, 6 conditioned Thoroughbred geldings performed a baseline SET and horses were assigned to one of 2 experimental treatment groups, placebo or ribose, based on VO2max. The placebo treatment group received 0.07 g glucose/kg bodyweight (bwt) and ribose treatment group received 0.07 g ribose/kg bwt top dressed on the feed twice daily. Following a 2 week treatment period, a second SET was performed. After a one-week washout period, the horses switched treatment groups. Following another 2 week treatment period, a third SET was performed. Blood ammonia-N was lower in the ribose treatment group at 15 min (P = 0.06) and 30 min (P = 0.02) postexercise. Plasma lactic acid was lower in the ribose treatment group at 30 min postexercise (P = 0.07). In Experiment 2, 1 h before a SET, 2 horses received 3 l water (control) and 3 horses 250 g of ribose dissolved in 3 l water (single ribose dose) via a nasogastric tube. Following a 2 week washout period, the horses switched treatment groups and another SET was performed. There were no differences in blood ammonia-N, plasma lactic acid or glucose between treatment groups. No differences in performance were detected between treatment groups in either experiment. In conclusion, the results from Experiment 1 show a trend that daily ribose supplementation may be beneficial during recovery from exercise. However, a single dose of ribose 1 h before exercise revealed no effect on the variables measured. Because moderate to intense daily exercise can cause a decrease in total adenine nucleotide (TAN) pool with no meaningful recovery even after 72 h rest, future experiments should be designed to futher elucidate the effects of ribose supplementation on TAN metabolism in horses exercising at high intensity.