Haemodynamic instability is one of the most frequent problems occurring during dialysis treatment. Ten clinically stable patients (8 M and 2 F) undergoing chronic maintenance haemodialysis for at least 6 months were investigated. Two groups of five patients each, were selected on the basis of presence (IG) or absence (SG) of cardiovascular instability during dialysis. The cardiovascular function was assessed by computerised electrical bioimpedance performed during dialysis setting and by echocardiography immediately pre- and post-dialysis. In SG dialysis treatment did not change cardiac index (CI), stroke index (SI) and systemic vascular resistances index (SVRI). However CI, SI and SVRI, tended to decrease in IG patients; the reduction in CI was primarily due to a decrease in SI. Ejection velocity index increased significantly in SG but not in IG. Evaluation of cardiac function by Döppler echocardiography revealed a significant increment in fractional shortening, mean velocity of circumferential fiber shortening and Suga' index in SG with dialysis but not in IG. Stress index decreased significantly in both groups. Hormonal and biochemical parameters were not significantly different before and after dialysis in both groups. In IG the decrease in mean blood pressure, due to a reduction of SI, recognises in the inadequate response of myocardial contractility to volume subtraction, the genesis of its drop. Finally, impedance cardiography in uraemic patients helps to identify the factors that contribute to the impairment of cardiac performance and that should be studied before selecting new and advanced dialysis programmes.