Serial measurements of plasma volume and ascites volume were made during treatment with large doses of oral diuretics in 14 patients with stable chronic liver disease. Eight patients had pitting edema in addition to ascites. Reproducibility of ascites and plasma volume measurements was verified in 10 control subjects not receiving diuretics. Six patients without edema undergoing rapid diuresis lost a mean of 1.2 +/- 0.2 L of ascites and an equivalent amount of weight (1.3 +/- 0.4 kg) per day. All had a rise in blood urea nitrogen or creatinine, or both, and a fall in creatinine clearance. Eight patients with edema undergoing rapid diuresis lost more weight (1.8 +/- 0.5 kg/day, p = 0.06) but less ascites (0.7 +/- 0.35 L/day, p less than 0.05) than those without edema, and none developed renal insufficiency. After edema disappeared, ascites mobilization increased (1.4 +/- 0.7 L/day) and renal dysfunction occurred. Plasma volume fell an average of 24% +/- 9% in patients without edema but did not change in patients with edema (-0.4% +/- 3%). When edema disappeared, plasma volume fell significantly (28% +/- 8%, p less than 0.001). Electrolyte changes including hyponatremia, hyperkalemia, and hypochloremia were seen only in the group without edema. Patients with ascites and no edema are able to mobilize more than 1 L/day during rapid diuresis, but at the expense of plasma volume contraction and renal insufficiency. Patients with peripheral edema appear to be protected from these effects because of the preferential mobilization of edema and may safely undergo diuresis at a rapid rate (greater than 2 kg/day) until edema disappears.