Background/ Aims: Patients with K/ DOQI stage 5 chronic kidney disease ( CKD) have higher incidence of cardiovascular events due to the oxidative stress and endothelial dysfunction ( ED). The aim of this study is to evaluate the effects of N- acetylcysteine ( NAC), which might prevent cardiovascular events by improving oxidative stress on endothelial cells in patients with CKD. Methods: Thirty uremic patients ( age 40 +/- 12 years, 6 males) on hemodialysis ( HD) were evaluated for ED by using high- resolution Doppler ultrasound of brachial artery before and after 6 weeks of oral NAC ( 2 x 600 mg) medication. Also, 13 healthy controls ( 35 +/- 9 years, 5 males) were included in the study. Reactive hyperemia following 5 min forearm ischemia was accepted as endothelium-dependent vasodilatation ( flow- mediated dilatation; FMD) and compared to endothelium- independent vasodilatation in response to sublingual glyceril trinitrate ( GTN). Results: Patients on HD had lower Delta FMD ( 0.28 +/- 0.17 vs. 0.41 0.11, p < 0.05) and FMD% ( 7.5 +/- 5.05 vs. 11.33 +/- 2.95, p < 0.05) than the controls. Baseline Delta GTN and GTN% were similar in two groups. NAC treatment significantly increased the Delta FMD ( 0.41 +/- 0.11, p < 0.001 vs. baseline) and FMD% ( 10.59 +/- 3.22, p < 0.01 vs. baseline) of patients on HD, while it had no effect on Delta GTN and GTN%. Conclusion: These results suggest that NAC treatment could improve the ED by preventing the reduction of FMD in patients on HD. Copyright (c) 2007 S. Karger AG, Basel.