Recent studies have addressed the influence of dietary nitrate supplementation on the physiological responses to exercise. We have shown that enhancing nitric oxide (NO) bioavailability through supplementation of the diet with nitrate-rich beetroot juice reduces resting blood pressure and the O2 cost of exercise and improves exercise performance. Specifically, we found that 4-6 days of nitrate supplementation (0.5 L of beetroot juice per day containing ~ 6 mmol nitrate) reduced the steady-state O2 cost of sub-maximal cycle exercise by 5% and extended the time-to-exhaustion during high-intensity cycling by 16%. These effects were highly surprising given that the O2 cost of sub-maximal exercise has been considered to be essentially fixed. We and others have subsequently confirmed these findings in other populations and with different exercise modalities. The positive effects of nitrate supplementation on the O2 cost of sub-maximal exercise can be manifest acutely (i.e. 2.5 h following ingestion) and this effect can be maintained for at least 15 days if supplementation is continued. Because beetroot juice contains compounds other than nitrate that might also be bioactive, we have developed a nitrate-depleted beetroot juice as a placebo. We found that nitrate-depleted juice had no physiological effects relative to a control condition whereas nitrate-rich beetroot juice reduced the O2 cost of both walking and running and extended the time-to-exhaustion by 15%. These results confirm that nitrate is the key bioactive component of beetroot juice, though it cannot be discounted that other components (such as antioxidants and polyphenols) facilitate the bioconversion of nitrate to NO. Most recently, we and others have investigated the influence of acute dietary nitrate supplementation on time trial (TT) performance in competitive cyclists. These studies have shown a 1-2% reduction in the time to complete TT distances between 4 and 16 km. The dose of nitrate that has been shown to improve exercise efficiency can readily be achieved through the consumption of 0.5 L of beetroot juice (or an equivalent high-nitrate foodstuff). Following a 5-6 mmol bolus of nitrate, plasma [nitrite] typically peaks within 2-3 h and remains elevated for a further 6-9 h before declining towards baseline. Therefore, it is recommended that nitrate is consumed approximately 3 h prior to competition or training. A daily dose of a high-nitrate supplement is required if plasma [nitrite] is to remain elevated. It is presently unclear how ustained dietary nitrate supplementation might impact upon adaptations to training. There is the possibility that uncontrolled high doses of nitrate salts might be harmful to health. In contrast, natural sources of nitrate are likely to promote health. For this reason, it is recommended that athletes wishing to explore possible ergogenic effects of nitrate supplementation employ a natural, rather than pharmacological, approach.