Endothelial function is impaired in renal allograft recipient. Immunological reaction, immunosuppressive therapy, hypercholesterolemia and hypertension by generating oxidative injury could destroy endothelial derived nitric oxide (NO). Antioxidant could reverse endothelial dysfunction and tea contains antioxidant flavonoid. Flow mediated vasodilatation (FMD) is an indirect way to estimate NO-dependent endothelial vasomotor function. To test this hypothesis that tea consumption could reverse endothelial dysfunction, we entered 15 (F 6/M 9, 24-50 years) stable renal transplant recipients (serum creatinin: 1.3+/- 0.39 mg/dl). Whole blood cyclosporine levels and serum cholesterol levels were (244+/-65 ng/ml) and (189+/- 43.3 mg/dl), all between 14-48 months after transplantation. Lipid lowering agent was stopped one week before the study. FMD of right brachial artery was measured by high resolution vascular ultrasound (7.5-MHZ linear-array transducer) at baseline and two hour after consumption of 10 gram black tea leaf, was brewed for 5 minutes with 0.5 liter water. All by one sonologist, after 8-12 hours fasting, in the morning. The day after basal FMD and two hour after consumption of 0.5 liter boiled water were measured again. Percentage of FMD increment in each condition was calculated. Brachial artery FMD improved from a base of 8.0+/- 3.8% (4.0+/-0.49mm to 4.3+/- 0.47mm) to 14.0+/-4.6% (4.0+/- 0.53mm to 4.6+/-0.55mm) after tea consumption (P<0.05). FMD was not improved significantly after water consumption: basal FMD of 7.3+/-3.8% (4.0+/-0.49mm to 4.3+/-0.44mm) increased to 7.6+/- 4.6% (4.0+/-0.50mm to 4.3+/-0.49mm), (P>0.05) Tea is a widely consumed beverage worldwide; this study demonstrates that shortterm black tea consumption improves NO mediated endothelial dysfunction in renal transplant recipients. It could improve cardiovascular mortality and morbidity in these patients.