The study will be conducted as a case-control study. Stable chronic kidney disease stage 5 patients on regular three times weekly maintenance dialysis were enrolled into the study after they had given written informed consent. The patient's concomitant medications were continued in an unchanged manner. Each patient underwent randomly one study week of three consecutive haemodiafiltration treatments with the polysulphone dialysis membrane. Haemodiafiltration were performed using Fresenius 4008 H monitors (Fresenius Medical Care, Bad Homburg, Germany). The ultrafiltration flow rate (QUF) of each session was set according to the individual patient's interdialytic weight gain. Anticoagulation was performed by unchanged adoption of the previous routine heparinization Treatment duration, QB and QD, as well as the infusion flow rate (QI) in post-dilution haemodiafiltration were kept constant for each patient for 3 months.At the silent of study, patients receiving OL-HDF were randomized into 2 arm,namely those with replacement volume ≦ 15 L & > 15 L.After 2 months, the replacement volume of the group with < 15 L replacement volumes will be increased to > 15 L for another 2 months (Group A). Those with >15 L replacement volumes will be kept unchanged(Group B). After a further 2 months, patients in group A will be randomized to take AST-120 for 3 months as shown in Figure 1All samples blood will be collected during the midweek dialysis from the AV fistula, immediately after the insertion of the dialysis cannula but before the administration of heparin. Blood was collected before dialysis on 3 occasions namely month 0, 3 and 6 m. Blood before dialysis was drawn Blood was sampled in 4 cc Venoject II tubes and centrifuged (10 min, 3000 r.p.m.). Serum were immediately stored at -20°C until assayed.