A rational approach to the diuretic therapy of ascites is proposed. Fifty-five patients were classified according to their ability to excrete sodium and free water. Patients with a high urinary sodium excretion can be treated by low sodium intake alone. In most patients with a low sodium excretion but high free water clearance, distal diuretics (spironolactone or triamterene) with a low sodium diet will relieve ascites. Patients with low values for sodium excretion and free water clearance also have poor glomerular filtration rate and only a few of these will respond to diuretic therapy.