1. 1. A simple liver function test is described which is based on the presence of excessive excretion of benzoyl glucuronate in the urine after ingestion of 5 Gm. of benzoic acid. The test is non-toxic and can be performed quickly. In selected cases, when used in conjunction with the current liver tests, it has important diagnostic application. 2. 2. The test was studied in twenty-three normal volunteers, in a control series of 100 patients who had no obvious hepatic disturbances, and in eighty-nine other patients in whom hepatic disturbances were suspected. 3. 3. In all normal volunteers, and in patients without hepatic disturbances the test was negative. 4. 4. In all cases of hepatitis and portal cirrhosis the test was positive. 5. 5. The test was also positive in some patients with thyrotoxicosis and in most cases of hepatic metastasis. It was negative in all of nine lymphomas. 6. 6. Application to two cases of early-type post-arsphenamine jaundice is described. In both cases hepatocellular damage was indicated by positive tests. In one the diagnosis of arsphenamine hepatitis was made in the presence of gallstones. 7. 7. The glucuronate reactions remained negative in a patient with obstructive jaundice of very long standing.