It has been suggested that a prior bout of high-intensity exercise has the potential to enhance performance during subsequent high-intensity exercise by accelerating the V_O2 on-response. However, the optimal combination of prior exercise intensity and subsequent recovery duration required to elicit this effect is presently unclear. Eight male participants, aged 18-24 yrs, completed step cycle-ergometer exercise tests to 80% of the difference between the pre-established gas exchange threshold and V_O2 max (i.e., 80%) following no prior exercise (control) and following six different combinations of prior exercise intensity and recovery duration: 40% with 3 min (40-3-80), 9 min (40-9-80), and 20 min (40-20-80) recovery; and 70% with 3 min (70-3-80), 9 min (70-9-80), and 20 min (70-20-80) recovery. The overall V_O2 kinetics was accelerated relative to control in all conditions except 40-9-80 and 40-20-80 as a consequence of a reduction in the V_O2 slow component amplitude; the phase II time constant was not significantly altered with any prior exercise/recovery combination. Exercise tolerance at 80% was improved by 15% and 30% above control in the 70-9-80 and 70-20-80 conditions, respectively, but was impaired by 16% in the 70-3-80 condition. Prior exercise at 40% did not significantly influence exercise tolerance regardless of the recovery duration. These data demonstrate that prior high-intensity exercise (~70%) can enhance the tolerance to subsequent high-intensity exercise provided that it is coupled with adequate recovery duration ( 9 min). This combination presumably optimizes the balance between preserving the effects of prior exercise on V_O2 kinetics and providing sufficient time for muscle homeostasis (e.g., muscle phosphocreatine and H⁺ concentrations) to be restored.