We have studied the efficacy of urea in the treatment of hyponatremia and hydrosaline retention in cirrhotic patients with ascites resistant to diuretics. In 5 patients with hyponatremia and ascites resistant to a major diuretic treatment (200-400 mg spironolactone combined with 40-160 mg furosemide/day for 4 of them), urea intake (30-90 g/day) induced the following changes: the daily weight changed from a gain of 0.01 +/- 0.06 kg/day to a loss of 1.03 +/- 0.12 kg/day (p less than 0.001) (mean +/- SEM), serum sodium concentration rose from 128 +/- 1.3 to 133 +/- 1.4 mmol/l (p less than 0.01), sodium output increased from 24 +/- 4 to 82.5 +/- 11 mmol/day, diuresis increased from 1.05 +/- 0.10 to 2.24 +/- 0.24 liters/day (p less than 0.01). Despite an important weight loss, the creatinine clearance did not change significantly (53.6 +/- 4.5 ml/min before and 70.0 +/- 8.2 ml/min during urea). In patients responding to classical diuretics, urea as a monotherapy was less effective. From the 6 patients with resistant ascites, only 1 developed prerenal uremia after urea treatment. In order to enhance urea efficacy, it is important to take it together with a long-loop diuretic. Intermittent urea intake seemed to be useful in cirrhotic patients with hyponatremia associated with ascites resistant to diuretics and with low or normal blood urea concentrations.