Supplementation with inorganic nitrate has been suggested to be an ergogenic aid for athletes as nitric oxide donor. The purpose of this study was to determine whether ingestion of inorganic sodium nitrate benefits well-trained athletes performing a 40-min exercise test in laboratory conditions. In addition, we investigated the effect of this supplement on plasma levels of endothelin-1 (ET-1) and in nitrated proteins. Thirteen trained athletes participated in this randomized, double-blind, crossover study. They performed a 40-min cycle ergometer distance-trial test after two 3-d periods of dietary supplementation with sodium nitrate (10 mg·kg of body mass) or placebo. Concentration of plasma nitrate (256 ± 35 μM) and nitrite (334 ± 86 nM) increased significantly (P < 0.05) after nitrate supplementation compared with placebo (nitrate: 44 ± 11 μM; nitrite: 187 ± 43 nM). In terms of exercise performance, there were no differences in either the mean distance (nitrate: 26.4 ± 1.1 km; placebo: 26.3 ± 1.2 km; P = 0.61) or mean power output (nitrate: 258 ± 28 W; placebo: 257 ± 28 W; P = 0.89) between treatments. Plasma ET-1 increased significantly (P < 0.05) just after exercise in nitrate (4.0 ± 0.8 pg·mL) and placebo (2.4 ± 0.4 pg·mL) conditions. This increase was significantly greater (P < 0.05) in the nitrate group. Levels of nitrated proteins did not differ between treatments (nitrate: preexercise, 91% ± 23%; postexercise, 81% ± 23%; placebo: preexercise, 95% ± 20%; postexercise, 99% ± 19%). Sodium nitrate supplementation did not improve a 40-min distance-trial performance in endurance athletes. In addition, concentration of plasma ET-1 increased significantly after exercise after supplementation with sodium nitrate.