Backgrounds: Transient endothelial dysfunction (brachial artery flow-mediated dilatation; FMD) was observed in residents and house staff after a 24-hour shift, including night duty. We examined the effect of continuous night duty, with its inevitable stresses and lifestyle changes, on endothelial function in apparently healthy medical personnels and relationship of oxidative stress and FMD change. Methods: In 18 young healthy interns and nurses (5 males, 13 females), the endothelial functions that were defined by FMD, as well as the high sensitive C-reactive protein (hsCRP) level and oxidative stress assay [concentration of NOx(NO2- , NO3-), cGMP, lipid peroxidation assay) from peripheral blood were examined. FMD, oxidative stress assay and hsCRP were examined twice in each subject : first, on a regular workday (with no previous of subsequent night shift, defined as baseline measurement of (FMD) and second, after a continuous 3-night shift. All examination were performed in the morning. Results: Hs-CRP was not changed after a continuous 3-night shift (0.34짹0.35 vs 0.59짹1.06). The FMD was significantly decreased after continuous 3-night shift (12.6짹3.0% vs 8.5짹2.3%)(p=0.003). Nitrate-mediated dilation (NMD) was decreased after continuous 3-night shift (23.3짹1.9% vs 18.0짹3.8%) (p=0.04). Final results including more volunteers data and oxidative stress assay will be presented. Conclusion: This study suggested that endothelial dysfunction was associated positively with night working shifts.