The positive interaction between diffusive and convective flux has suggested that hemodiafiltration (HDF) has a higher oxalate extraction rate as compared with hemodialysis (HD). However, it has not been evaluated whether HDF can lower predialysis oxalate levels below the level of supersaturation. By using an intra-individual approach with the inclusion/exclusion criteria listed for the study, we plan to determine plasma oxalate and cytokine levels in 20 patients (10 on regular duration HD, 10 patients on extended duration HD) before dialysis. Subsequently, patients will be switched to HDF and plasma oxalate concentration and cytokines will be analyzed again two weeks following HDF treatment. Plasma oxalate (Pox) will be measured at beginning of treatment, mid, end and 2 hrs post treatment (to determine rebound) in order to provide oxalate kinetics on HD/HDF treatment. Cytokines will only be measured pre HD/HDF treatment to assess steady state inflammation.