The effect of dietary creatine (Cr) supplementation on performance during 3, 30 s bouts maximal isokinetic cycling and on plasma ammonia and blood lactate accumulation during exercise was investigated. Placebo (P) ingestion had no effect on peak power output (PPO), mean power output (MPO) and total work output during each bout of exercise. Cr ingestion (4 x 5 g.day-1 for 5 days) significantly increased PPO in exercise bout 1 (p < 0.05) and MPO and total work output in exercise bouts 1 (p < 0.05, p < 0.05, respectively) and 2 (p < 0.05, p < 0.05, respectively). Cr ingestion had no effect on any of the measures of performance during exercise bout 3. No difference was observed in peak plasma ammonia accumulation before (146 + 30 mumol.l-1) and after (122 +/- 17 mumol.l-1) P ingestion, however the corresponding concentration was lower following Cr ingestion (129 +/- 22 mumol.l-1) compared with before Cr ingestion (160 +/- 18 mumol.l-1, p < 0.05), despite subjects performing more work. No difference in peak blood lactate accumulation was observed before and after P or Cr ingestion. The results demonstrate that Cr ingestion can increase whole body exercise performance during the initial two, but not a third, successive bout of maximal exercise lasting 30 s. The lower accumulation of plasma ammonia under these conditions suggests this response is achieved by an effect on muscle ATP turnover.