Hypochloruria is proposed as an indicator of hypovolemia in ICU non cardiac patients. Twelve of 13 patients presenting with Clu less than or equal to 20 mmol X l-1 and Nau greater than or equal to 20 mmol X l-1 or twice the Clu value had a CVP less than or equal to 0 mmHg. This pattern occurred in those with a metabolic alkalosis or acidosis, renal insufficiency or normal renal function, in the presence or absence of dopamine and/or diuretic administration and with or without controlled ventilation. Hypochloruria may be a better indicator of hypovolemia than a low urinary Na in ICU patients.