With the urine of the patient with mechanical jaundice the author isolated direct bilirubins, both ester form and salt form, by the toutine techniques employed in our laboratory, and studied the realtionship between glucuronic acid and these bilirubins. 1. Regardless of the techniques used in isolating direct bilins of salt form the glucuronic acid reaction proves to be always negative. 2 Of the direct bilirubins of ester form, the one isolated by Komuta's precipitation method is negative to the glucuronic acid test. 3. Of direct bilirubins of ester form obtained by the ion-exchange chromatography as well as by butanol extraction method, most of them are positive to the glucuronic acid test but some prove to be negative. 4. By paper and column chromatography it has been possible to isolate from the esterform direct bilirubin fractions positive to glucuronic acid the direct bilirubin that is related to glucuronic acid aside from the ester-form direct bilirubins, but the quantity is trivial. From these results the existence of bilirubin glucuronide as contended by Billing et al can be understandable, but its quantity is an extremely small portion of the total ester-form bilirubins, and almost all of them prove to be what we in our laboratory call "ester-form direct bilirubins"