Hemofiltration and hemodiafiltration are two modes of extra-renal therapy which characteristics are: high efficiency, biocompatibility, good tolerance, low morbidity. On-line preparation of substitution fluid from sterile and apyrogen dialysate and modelization lead to propose in the futur HF ou HDF for all patients. Adequacy of epuration is not enough defined to conclude that HDF is better than HF.