Sterile dialysate, free of endotoxin (ET) and other cytokine inducing factors, will probably become a future standard. High-flux dialysis with bicarbonate and reuse has the membrane, the pressures, and bacteriologic potential for ET fragments to pass from dialysate to the blood side of the membrane with activation of monocytes and production of cytokines. Ultrafiltration through polysulfone filters has been shown to remove bacteria, ET, and its fragments and other cytotoxic inducing factors. The authors found that in spite of sterile, ET-free, reverse osmosis (RO) water, ET was usually present at the dialyzer inlet and arose from the RO storage tank water with bacteria < 30 CFU/ml, in spite of repeated disinfection. The authors now remove bacteria, ET, and fragments from RO tank water with a 5 mu cellulose filter followed by ultrafiltration with a Fresenius F-80 polysulfone dialyzer inserted between the wall RO delivery port and each delivery system. At the dialyzer inlet, monthly bacterial counts were < 30 cfu/ml, and ET values (n = 38) were not detectable in 89% and < 0.5 EU/ml in 11%. The F-80 filters were used for 180+ dialyses along with the 5 mu filters, which replaced the frequently endotoxin contaminated 10 mu filters in the Monitral-S delivery systems. The costs did not increase.