The mortality and morbidity of hemodialysis patients is, to a large extent, determined by demographics and by existing comorbidities, but it is obvious that variations in dialysis dose have substantial effects. Using eKt/V, 1.2 monthly comparisons are recommended by European guidelines, but they assume that dose is maintained during all monthly sessions. Because of dialysis-related problems like hypotension, reduction of blood flow, dialysis time, microclotting of the dialyzer, and vascular access problems, the delivered dose may vary from session to session. New developed devices based on online conductivity clearance reflect the electrolyte clearance and, thus, clearance of urea. The aim of this prospective study was to show the variability of dialysis dose. 24 anuric patients were studied during 3 months: 20.8% were diabetics, mean age 64.7 ± 18.2 years; 16% females. Access blood were AVFi and the effective dialyzed blood flow was set at 350 mL/min, with recirculation <5%. BMI was 25.4 ± 3.8 kg/m2 and body weight was 69.7 ± 12 kg. All patients were dialyzed thrice weekly (245 ± 21 min) with dialysis machine 4008H (Fresenius Medical Care) equipped with online conductivity monitor (OCM) and the hollow fiber high-flux polysulfone membrane (HF-80 1.8 m2) and helixone (Fx-60, 1.6 m2). OCM was validated for our population and reported in other abstracts (r2 = 0.96, p < 0.001). Dialysate flow was maintained at 500 mL/min, with standard dialysate liquid. Each patient was subjected to OCM on regular sessions during 3 months, and blood Kt/V samples were taken on midweek day, once a month. Data were processed and statistically analyzed with SPSS 11.0 software package. Kt/V OCM relation with other baseline characteristics was assessed by using contingency tables, t-tests, analysis of variance, and linear regression, as appropriate. All the tests were performed for a 0.05 significance level. The conductivity-based OCM provides an accurate tool to monitor the dose and control of each hemodialysis session and adds to the efficiency of current dialysis adequacy monitoring. OCM device requires little maintenance, and no extra effort is needed. Monthly Kt/V does not reflect the variability of each session. Further studies are necessary to evaluate its influence on morbidity and mortality.