The "gold standard" method to measure the mass balance achieved during dialysis for a given solute is based on the total dialysate collection. This procedure is unfeasible and too cumbersome. For this reason, alternative methods have been proposed including the urea kinetic modelling (Kt/V), the measurement of effective ionic dialysance (Diascan), and the continuous spent sampling of dialysate (Quantiscan). The aim of this study was to compare the reliability and agreement of these two methods with the formulas proposed by the urea kinetic modelling for measuring the dialysis dose and others haemodialysis parameters. We studied 20 stable patients (16 men/4 women) dialyzed with a monitor equipped with the modules Diascan (DC) and Quantiscan (QC) (Integra. Hospal). The urea distribution volume (VD) was determined using anthropometric data (Watson equation) and QC data. Kt/V value was calculated according to Daurgidas 2nd generation formula corrected for the rebound (eKt/V), and using DC (Kt/VDC) and QC (Kt/VQC) data. The total mass of urea removed was calculated as 37,93 +/- 16 g/session. The VD calculated using Watson equation was 35.7 +/- 6.6 and the VDQC was 35.06 +/- 9.9. And they showed an significative correlation (r:0,82 p < 0.001). The (VDQC-VDWatson) difference was -0.64 +/- 5.8L (ns). Kt/VDC was equivalent to those of eKt/V (1.64 +/- 0.33 and 1.61 +/- 0.26, mean difference -0.02 +/- 0.29). However, Kt/VQC value was higher than eKt/V (1.67 +/- 0.22 and 1.61 +/- 0.26 mean difference 0.06 +/- 0.07 p < 0.01). Both values correlated highly (R2: 0.92 p < 0.001). Urea generation (C) calculated using UCM was 8.75 +/- 3.4 g/24 h and those calculated using QC was 8.64 +/- 3.21 g/24 h. Mean difference 0.10 +/- 1.14 (ns). G calculated by UCM correlated highly with that derived from QC (R2: 0.88 p < 0.001). In conclusion, Kt/VDC and Kt/VQC should be considered as valid measures for dialysis efficiency. However, the limits of agreement between Kt/VQC and eKt/V were closer than Kt/VDC.