It has been suggested that high inspiratory oxygen concentrations during anesthesia may be associated with higher postoperative mortality due to endothelial dysfunction. A randomized controlled crossover study was conducted with 25 healthy male volunteers. They inhaled an oxygen concentration of 30% and 80%. The endothelial function was assessed using noninvasive digital pulse amplitude tonometry (EndoPAT) supported by endothelial biomarkers. The difference in endothelial function between the 2 treatments was 0.05 (95% confidence interval,-0.36 to 0.27; P =.77). Endothelial biomarkers were unaffected. Inhalation of a high oxygen fraction in healthy volunteers did not result in a significant reduction of endothelial function.