Previous experimental research showed an attenuated vasoconstrictor response after acute exercise. This study aims to determine the effect of aerobic physical exercise on the endothelium-derived circulating nitric oxide (NO) concentrations among healthy young persons. A total of 10 subjects (5 men and 5 women) aged 21-28 were examined for the difference in concentrations of serum and plasma NO metabolites (NOx) before and after a single bout of aerobics, in which they performed cycling exercises at a constant workload corresponding to 90% of the subject-specific anaerobic threshold. A paired t-test resulted in no statistically significant differences between pre- and post-exercise concentrations of serum or plasma NOx. It is suggested that the acute effect of aerobic exercise on the vasoconstrictor/vasodilator response is not mediated by an increase in the endothelial NO release.