The tolerance to high levels of ultrafiltration that has been observed when using a RP-6 dialyzer with polyacrylonitrile membrane and a closed batch dialysate delivery system has led the authors to put patients on a free sodium and fluid intake. Eight patients were put on such a diet for six months. They have been dialyzed four to five hours, three times per week, on a RP-6-Rhodial 75. The mean intersession weight gain was 4.29+/-0.18 Kg after three days for a mean predialytic body weight of 63.55+/-2.54 Kg. Mean predialytic blood pressure was 1.38+/-4 mmHg for systolic pressure and 82+/-5 mmHg for diastolic pressure. Mean ultrafiltrate volume was 4.86+/-0.36 liters which corresponds to a sodium output of 661.3+/-49.5 mEq. Total plasma protein and hematocrit increased 18.8+/-3.34% and 19.13+/-3.22%, respectively, when the pre and post-dialytic values were compared. No clinical sign of fluid overload (dyspnea, edema, etc.) was noted in these patients. Cardiothoracic index remained in the normal range. This tolerance is due, possibly, to the high sodium concentration (145 mEq/L) in the dialysate. The free sodium and water diet may contribute to a better rehabilitation.