Central venous catheters are commonly used for haemodialysis patients and represent, in our centre, about 15% of the permanent vascular accesses with a total number of more than 230 central venous catheters over the last 10 years. Inadequate blood flow may occur and upsets the nurses, the patients, and the nephrologist. The aim of this study was to identify the factors of the catheter dysfunction. We studied prospectively 25 chronic haemodialysed patients with central venous catheters, 14 women and 11 men, 65 +/- 16 (55-89) years of age, treated with haemodialysis for 6.7 +/- 7 (1-26) years. Catheters were tunnelled silicone twin catheters (Permcath Quinton n = 18, Twincath Hemotec n = 7) in right (n = 19) and left internal jugular (n = 6) inserted by percutaneous Seldinger techniques. We studied the localization of the catheter tip (superior vena cava, right atrium, right ventricular, inferior vena cava), the central venous pressure before and after haemodialysis, the blood pressure (BP) before and after haemodialysis, the interdialytic weight gain, the number of symptomatic hypotensions during the 10 last dialyses. The patients were divided into two groups: group I with usual adequate catheter function (n = 18) and group II with frequent dysfunctions (n = 7). Central venous pressure before dialysis was significantly higher in group I with adequate blood flow and the catheter's tip was more frequently found localized in the right cardiac cavities than in the vena cava. When central venous pressure before dialysis was over 5 mmHg, no dysfunction occurred. Blood pressure was not different between the two groups. We found no correlation between central venous pressure and BP, interdialytic weight gain and symptomatic hypotensions. We could not predict the central venous pressure from the mean BP but there was a higher frequency of hypotensions in the hypovolaemic patients. Optimal haemodynamic conditions will be provided by a catheter tip in the right cardiac cavities and a central venous pressure over 5 mmHg which can be provided with vascular filling or dry weight revaluation.