The exchange of purines in exercised and rested muscle and their relation to muscle ATP levels after intense intermittent exercise were investigated. Seven subjects performed one-legged knee extensor exercise on the following two occasions: without (control; C) and with (high purines; HP) additional arm exercise. There was a greater net release of hypoxanthine by the exercised muscle during the recovery period in HP compared with C [185 +/- 44 vs. 101 +/- 30 (SE) mumol/kg muscle; P < 0.05]. During recovery, the arterial urate concentration was higher in HP compared with C (peak: 585 +/- 48 vs. 355 +/- 20 mumol/l; P < 0.05). The exercised but not the rested muscle extracted a marked amount of urate (330 mumol/kg muscle) from plasma in the HP trial. Muscle ATP levels after 90 min of recovery in HP were lower than at rest (24.3 +/- 0.6 vs. 20.1 +/- 1.1 mmol/kg dry wt). The present data suggest that a single session of long-term high-intensity intermittent exercise causes a significant release of purines from the muscle into blood, which contributes to a sustained lowered level of the muscle ATP concentration. Furthermore, intensely exercised muscle extracts urate when plasma urate is elevated, an event that may be of importance for the replenishment of oxidized muscle urate stores.