The purpose of this study was to determine the effects of acute L-arginine supplementation on the endothelial health in healthy adults by assessing flow-mediated dilation (FMD) and cardiovascular indicators both before and after resistance exercise to fatigue. Thirty (15 male, 15 female) physically active healthy participants (mean ± SD: age 20.4 ± 1.8 years, height 176.9 ± 10.2 cm, body mass 76.0 ± 12.2 kg) volunteered for a randomized, cross-over, double-blind, placebo controlled clinical trial. Participants completed five sets of isokinetic elbow extension/flexion exercise after consumption of either placebo or 3 g L-arginine one hour prior. Baseline brachial artery diameter significantly increased post FMD (p<0.001), post-exercise (p<0.001), post-exercise FMD (p<0.001). There was no significant supplement effect on FMD (p=0.179). The increase in brachial diameter due to fatiguing exercise was not enhanced by acute supplementation with L-arginine nor did supplementation alter FMD responses after exercise.