Purpose: The objective of this study is to examine the effects of acute ingestion of dietary nitrate on endurance running performance in highly trained cross-country skiers. Dietary nitrate has been shown to reduce the oxygen cost of submaximal exercise and improve tolerance of high-intensity exercise, but it is not known if this holds true for highly trained endurance athletes. Methods: Ten male junior cross-country skiers (V̇O2max 70 mL•kg•min) each completed two trials in a randomized, double-blind design. Participants ingested potassium nitrate (614-mg nitrate) or a nitrate-free placebo 2.5 h before two 5-min submaximal tests on a treadmill at 10 km•h-1 (55% of V̇O2max) and 14 km•h -1(75% of V̇O2max), followed by a 5-km running time trial on an indoor track. Results: Plasma nitrite concentrations were higher after nitrate supplementation (325 ± 95 nmol•L) compared with placebo (143 ± 59 nmol•L, P < 0.001). There was no significant difference in 5-km time-trial performance between nitrate (1005 ± 53 s) and placebo treatments (996 ± 49 s, P = 0.12). The oxygen cost of submaximal running was not significantly different between placebo and nitrate trials at 10 km•h (both 2.84 ± 0.34 L•min) and 14 km•h (3.89 ± 0.39 vs. 3.77 ± 0.62 L•min). ConclusionS: Acute ingestion of dietary nitrate may not represent an effective strategy for reducing the oxygen cost of submaximal exercise or for enhancing endurance exercise performance in highly trained cross-country skiers. © 2012 by the American College of Sports Medicine.