BACKGROUND Hemodynamic stability of patients during dialysis sessions is of pivotal importance in daily practice and accurate determination of dry weight (DW) remains a challenge. Little information is available about central venous and aortic pressure during dialysis. In this pilot study we used a new non-invasive technique to describe the changes in central venous pressure (CVP) during dialysis. METHODS An ultrasound-assisted silicon-based pressure-manometer was used at the contralateral cephalic vein during haemodialysis to quantify central venous pressure. Central aortic pressure changes were assessed as aortic augmentation index (AIx) and subendocardial viability ratio (SEVR) by radial applanation tonometry and brachial arterial blood pressure measurements. Bioimpendance was applied to measure total body water (TBW), as well as extracellular (ECW) and intracellular (ICW) water before and after HD. All measurements were performed prior during and after one and two hours on HD except for bioimpedance that was only assessed before and after dialysis. RESULTS Ten patients (5 female) were included with a median age of 72 years (23-82). Haemodialysis reduced the weight by 2.0 kg (range 0.2 - 3.9 kg), corresponding to a measured decrease in TBW of 1.9 L (36.1 L to 34.2 L, n.s.). The mean CVP showed a significant decrease (9.0 cmH2 O to 0.8 cmH2 O; p=0.0005) during dialysis. The major and significant drop in CVP was found during the first hour of haemodialysis (9 cmH2 O to 2.8 cmH2 O). Starting and stopping dialysis was reflected by a reduction of 2.6 cmH2 O and a rise of 2.8 cmH2 O (n.s.). AIx decreased continuously from 26.1 % to 21.0 % (n.s.). SEVR increased significantly from 126 % to 156 % (p<0.05) during HD, and decreased to 139% direct after HD (n.s.). CONCLUSIONS This is the first study that illustrates a prominent reduction of central venous pressure during the first hour of hemodialysis. Non-invasive central venous pressure measurement is feasible during hemodialysis and adds another piece in the puzzle of factors involved in hemodynamic stability.