Paired hemodiafiltration (PHF) is a dialysis modality where an ultrafilter and a filter with hollow-fiber membranes are used in series for on-line infusion of ultrapure fluid. PHF is a on-line hemodiafiltration modality which allows reinfusion using the dialysate prepared by the monitor. The dialysate is infused by retrofiltration, which takes place in the filter positioned in series with regard to the filter where ultrafiltration and the diffusive/convective exchange of solutes occur. The indications and contraindications of the method are the same as those of standard on-line hemodiafiltration, but PHF minimizes the inflammatory response of the patient. This is the result of the increased number of ultrafiltration stages (three), two of which in the monitor and the third by the filter in series, where the retrofiltration takes place. The method can also be carried out with acetate-free dialysate; this reduces the side effects of acetate used to stabilize pH in bicarbonate dialysate, resulting in better cardiovascular stability during dialysis.