The purpose of this study was to investigate the influence of intense exercise on the metabolism of adenine nucleotides in the liver. In the first experiment, to determine the degradation of adenine nucleotides, hepatic adenine nucleotides of rats were labeled by an intraperitoneal administration of ¹⁵N-labeled adenine the day before treadmill running to exhaustion. In the second experiment, to determine the de novo synthesis of purine nucleotides after intense exercise, ¹⁴C-glycine was intraperitoneally administered to rats performing intense running on a treadmill. In the first experiment, hepatic levels of ATP and total adenine nucleotides showed a reduction immediately after exercise. In contrast, hepatic levels of AMP, adenosine, hypoxanthine and uric acid showed an increase immediately after exercise. The hepatic ¹⁵N level continued to decline during the recovery period after exercise. Urinary excretion of ¹⁵N-urate was 40% higher in the exercised rats than in the control rats. In the second experiment, the radioactivity of ¹⁴C detected in the fraction of hepatic urate and allantoin was approximately 300% higher in the exercised rats than in the control rats. ¹⁴C-radioactivity that excreted into urine as urate and allantoin was approximately 200% higher in the exercised rats. Intense exercise led to the degradation of hepatic adenine nucleotides, which were not utilized for the re-synthesis of nucleotide and further degraded to hypoxanthine or uric acid. Intense exercise induced the synthesis of purine nucleotides in the liver via a de novo pathway and these synthesized nucleotides were also degraded to nucleosides and excreted into urine.