Seven male subjects performed repeated bouts of high-intensity exercise on a cycle ergometer, before and after 6 days of creatine supplementation (20 grams Cr Monohydrate per day). The exercise protocol consisted of five 6-sec. exercise periods performed at a fixed exercise intensity, interspersed with 30-sec. recovery periods (Part I), followed (40-sec. later) by one 10-sec. exercise period (Part II) where the ability to maintain power output was evaluated. Muscle biopsies were taken from m. vastus lateralis at rest, and immediately after (i) the fifth 6-sec. exercise period in Part I and (ii) the 10-sec. exercise period in Part II. In addition, a series of counter movement (CMJ) and squat (SJ) jumps were performed before and after the administration period. As a result of the creatine supplementation, total muscle creatine [creatine (Cr) + phosphocreatine (PCr)] concentration at rest increased from (mean ± SEM) 128.7 (4.3) to 151.5 (5.5) mmol per kg dry wt (P <0.05). This was accompanied by a 1.1 (0.5) kg increase in body mass (P < 0.05). After the fifth exercise bout in Part I of the exercise protocol, PCr concentration was higher [69.7 (2.3) vs. 45.6 (7.5) mmol per kg dry wt. P < 0.05] and muscle lactate was lower [26.2 (5.5) vs. 44.3 (9:.9) mmol kg-' dry wt, P < 0.05] after vs. before supplementation. In Part II, after creatine supplementation, subjects were better able to maintain power output during the 10-sec. exercise period (P <0.05). There was no change in jump performance as a result of the creatine supplementation (P >0.05). These findings show that enhanced fatigue resistance during short duration high-intensity exercise following creatine supplementation is associated with a greater availability of PCr and a lower accumulation of lactate in the muscle. The finding that jump performance was not enhanced suggests that short-term creatine feeding does not influence peak power output.