Medical treatment of ascites is aimed at reverting sodium retention, that is, at creating a negative sodium balance to relieve ascites. Bed rest and low-sodium diet induce the disappearance of ascites in about 10% of patients. Loop diuretics and aldosterone antagonists must be administered to the patients not responding to the previous regimen. Available evidence indicates that aldosterone antagonists are the first-choice drugs, as these substances are more effective than furosemide. Nevertheless, loop diuretics potentiate the effects of aldosterone antagonists. The reduced efficacy of furosemide in these patients, when compared with that of spironolactone, may be related to an impairment of both pharmacodynamics and pharmacokinetics. In fact, most sodium not reabsorbed in Henle's loop, due to the action of furosemide, is subsequently taken up in the distal nephron because of hyperaldosteronism. A further mechanism of resistance may be related to an impaired excretion of furosemide into the tubular lumen. The use of diuretics in the treatment of ascites is associated with several side effects, including prerenal azotemia, hepatic encephalopathy, and electrolyte and acid-base disorders. A stepped-care approach, together with careful monitoring of patients, is the best way to reduce the incidence of these complications. Ethacrynic acid has been shown to be highly effective in the treatment of ascites, even in patients refractory to other diuretics, but its use is associated with a high incidence of hypokalemia and hypochloremic alkalosis. Bumetanide and piretanide are comparable to furosemide, in terms of both efficacy and side effects.(ABSTRACT TRUNCATED AT 250 WORDS)