The amount of potassium removed during a dialysis session depends on the potassium gradient between dialysate and blood, the duration of the session, the pH of the dialysate (bicarbonate content), and the presence or not of glucose in the dialysate. The last one, although theoretically known as a parameter that affects potassium removal during the dialysis session, is not known to what extent it affects. The aim of this study was to investigate how much potassium is lost with predilution online hemodiafiltration (with dialysate with or without glucose). We studied in 27 hemodialyzed patients the removal of potassium by a polyethersulfone dialyzer. Fourteen of them were males and the rest females. The median age of the patients was 73 years (range 54 - 93). They were on dialysis for 83.2 ± 87.6 months (range 14 - 450). We investigate the removal of potassium by predilution online hemodiafiltration with glucose in dialysate (Group A) and without glucose (Group B). We noted significant lower amount of potassium removed in patients of group A in comparison with those in group B (28.3 ± 18.6 Vs 38.1 ± 22.4 mmol, p < 0.02). Of these patients, those who followed their diet meticulously (n=10) and were consistent with the diet instructions had very little potassium loss/session (from 0 to 20 mEq), mainly in the first case (dialysate with glucose). It is highlighted that 9 patients of group A loss glucose during the session (6.4 ± 4.7 g/session, from 1.4 to 18.4). The amount of glucose removed during the dialysis session in group B was 63.4 ± 27.0 g (from 13.3 to 133.4 g/session), along with some mild adverse events of hypoglycemia. It is concluded that the amount of potassium loss during predilution online hemodiafiltration with glucose in dialysate is significantly lower than the loss with dialysate without glucose. Also, in dialysis with glucose in dialysate, some patients lose glucose during the session, while with a glucose-free dialysate, quite significant amounts of glucose are lost (with the risk of hypoglycemia occurring).