3 patients with hepatic cirrhosis and ascites underwent increased diuresis on six occasions, closely related to episodes of gastrointestinal bleeding. In each instance the increased urine volume was preceded by a sharp increase in blood urea nitrogen, presumably due to absorption of nitrogenous compounds from the gastrointestinal tract, suggesting a mechanism of osmotic diuresis. In each case there was a signigicant increase in serum sodium and osmolality, related to the greater-water-than-sodium diuresis induced by urea, which was promptly reversed by the administration of water or isotonic solution. Clinically this syndrome may be defined as the association of hypernatremia and hyperosmolality due to osmotic diuresis from urea appearing in a cirrhotic patient with ascites and gastrointestinal bleeding.