The Authors have evaluated the possibilities of use of the PFD in the regular dialysis treatment. At first they have studied in 8 patients the advantages offered by this technique in terms of depuration of small molecules and of tolerance in comparison with HD and HDF. Subsequently, they have compared the performances obtained in HF in a second group of 7 patients with the results observed in PFD executed by using 2 dialyzers on line and, in a second phase, in parallel, extending the comparison parameters to a higher molecular weight solute such as the beta 2-M. The results obtained indicate the PFD as a technique which can offer (compared to HD) a better tolerance and higher depurative performances, which on their turn can eventually allow a reduction of the length of the treatment. Moreover the possibility of executing the PFD with 2 polysulfone dialyzers on line and in parallel, increasing the UF to 13.5 and 15 L, renders this technique competitive with the HF also for its capacity of removing the beta 2-M.