In order to assess potential acute beneficial effects of flavanols in patients with ESRD, 10 patients undergoing dialysis will be recruited. Subjects will receive a cocoa drink with 16 mg, 250 mg, and 500 mg (in 100 mL water each) flavan-3-ols (40% epicatechine/catechine und 60% procyanidine), respectively, on three consecutively days. The functional/hemodynamic parameters (flowmediated dilation (FMD), venous-occlusion-plethysmography (VOP), blood pressure, heart rate), the biochemical marker of the circulating NO pool (nitrite, nitrate, RNOs), and the plasma levels of flavanols (epicatechine and catechine) will be determined before and after ingestion of the respective cocoadrink.