A key feature of dialysis treatment is the prescription of dialysate sodium (Na). This study aimed to describe the practical implementation of a new automated dialysate Na control biosensor and to assess its tolerance and the beneficial clinical effects of isonatraemic dialysis. A prospective study was carried out in 86 patients who, along with their usual parameters, received the following five consecutive phases of treatment for 3 weeks each: phase 0: baseline 5008 machine; phases 1 and 2: 6008 machine without activation of the Na control biosensor and the same fixed individualized Na dialysate prescription or adjusted to obtain similar conductivity to phase 0; phases 3 and 4: activated Na control to isonatraemic dialysis (Na dialysate margins 135-141 or 134-142mmol/L). When the Na control was activated, the few episodes of cramps or hypotension disappeared when the lower dialysate Na margin was increased by 1 or 2mmol/L. The activated Na control module showed significant differences compared with baseline and the non-activated Na module in final serum Na values, diffusive Na balance, and changes in pre- to postdialysis plasma Na values. The mean predialysis systolic blood pressure value was significantly lower in phase 4 than in phase 1. There were no significant differences in total Na balance in the four 6008 phases evaluated. The implementation of the automated dialysate Na control module is a useful new tool, which reduced the diffusive load of Na with good tolerance. The module had the advantages of reducing thirst, interdialytic weight gain and intradialytic plasma Na changes.