The patients enrolled were randomized into two groups of treatments lasting six weeks each. Group A: 1st and 2nd weeks with bicarbonate dialysis and filter PMMA, 3rd and 4th weeks with filter HFR17, 5th and 6th weeks with bicarbonate dialysis filter F7. Group B: 1st and 2nd weeks with filter HFR17, 3rd and 4th weeks with bicarbonate dialysis and filter PMMA, 5th and 6th weeks with bicarbonate dialysis filter F7. The dialysis sessions carried out during weeks 1, 3 and 5 were considered washout sessions between weeks 2, 4 and 6 when the assessment of lambda and k light chains, β2M, C reactive protein and albumin was scheduled. Week number 1 was the washout period between the usual dialytic treatment of the patients enrolled and the beginning of the study. The checking dialysis session was the midweek session and the blood was drawn on starting dialysis (time 0), at two hours (time 120') and at dialysis end (time 240'). All the dialysis sessions lasted four hours. Mean blood flow was 310±30 ml/min, the mean ultrafiltration rate was 700±200 ml/h, during HFR the endogenous ultrafiltrate rate was 2.3±0.4 ml/h. Dialysate flow was 500 ml/min. Low molecular weight heparin enoxaparin (Clexane®, Sanofi, Milan, Italy) was used for anticoagulation of the extracorporeal circuit. Doses of 2000 IU (patients <50 kg of body weight), 4000 IU (patients between 50 to 90 kg of body weight) or 6000 IU (patients >90 kg of body weight) were administered in a single bolus on starting dialysis. Fresenius 5008 and Bellco Flexya dialysis machines were used. The concentrations of k and lambda light chains and β2M were measured by nephelometry (kit Freelite k/lambda, The Binding Site Group Ltd., Birmingham, United Kingdom; IIMAGE/IMMAGE 800 Beckman Coulter instrument, Brea California USA, Beckman Coulter β2M kit). Normal values: k light chains 3.3 -19.9 mg/L, lambda light chains 5.7-26.3 mg/L, β2M 0.7 - 2 mg/L. Molecular weights: k light chains: 22,500 daltons; lambda light chains: 45,000 daltons; β2M: 11,818 daltons. The reference range for patients with normal kidney function was considered between 0.26 and 1.65 according to Bourguignon et al.. CRP concentration was measured by turbidimetry (CRPLX, Tina-quant C-Reactive-Protein; Roche/Hitachi 902 analyzer). CRP normal value < 0.8 mg/dl, molecular weight 120,000 daltons. Albumin was assessed using the common laboratory method. The reduction rate per session (RRs) was calculated as follows: