Participants will receive outpatient hemodialysis 3 times a week using B. Braun CE0123 machines (B. Braun, D-34212 Meisungen, Germany). All patients will use B. Braun polysulfone membranes. To control for the effects of volume on blood pressure and the RAS, we plan to keep target postdialysis weight (dry weight) constant for each patient during the study. Dialysate sodium concentrations will be held constant at 140 mEq/L for all patients, dialysate potassium concentrations will be maintained at 2 mEq/L thru the study. We do not plan to impose additional dietary potassium restrictions beyond the usual recommendations for patients with ESRD treated with hemodialysis. We plan to make no changes to dialysate potassium concentrations or antihypertensive regimens. Because of a mandate not to alter the antihypertensive regimen, target weight, and dialysis potassium bath during the study, we will exclude patients with hypotension, severe hypertension, and hyperkalemia. To evaluate the effect of Eplerenone independent of its diuretic action, we plan to include only oliguric or anuric patients (urine output <500 mL/24 h).