The estimation of dry weight in dialysis patients remains a difficult task. In this study we examined whether the relationship between a raised central venous pressure (CVP) and a pulsatile flow in the femoral vein could be useful to assess dry weight in dialysis patients. 26 dialysis outpatients had their femoral vein flow measured by Doppler ultrasonography every half hour during dialysis. 40 dialysis inpatients had both their femoral vein flow and the inferior vena cava diameter (IVCD), as well as their CVP measured before, in the middle and after dialysis. The absence of pulsatile flow in the femoral vein before dialysis correlated in a statistically significant way to low CVP and small IVCD. It was thus demonstrated that those patients were close to their dry weight. On the other hand, the presence of a pulsatile flow CANNOT be clearly interpreted as a sign of fluid overload. It can be caused by right heart failure and it can be occasionally observed in healthy individuals. After dialysis, however, the relationship between CVP, IVCD and the flow in the femoral vein was not as clear as before dialysis. A quantitative analysis based on indices computed in a way similar as in arterial Doppler ultrasonography was not possible, since the venous flow is influenced by several phenomena, such as inspiration and expiration. Provided that the limitations of the method are understood and taken into account, the simple and reproducible technique used in this study, namely the Doppler ultrasonography of the femoral vein, can be successfully applied in estimating dry weight of dialysis patients. Especially, the method can unequivocally identify underhydration in dialysis patients.