The properties of so-called ether extractable bilirubin were studied, and the following results were obtained: 1. In comparing the pigment extracted by adding ether to jaundiced serum with crystalline bilirubin, some remarkable differences were observed between the ether solutions of them both, that is, differences in an absorption curve, a diazo reaction, and the reactions to acid and alkali. 2. The ether solution was found to contain both direct and indirect reacting bilirubins, the former taking the greater part in quantity. 3. This direct reacting bilirubin was considered to be of ester in type which we call ester-type bilirubin as it was presumed to have a phosphate ester, showing its absorption maximum at 415 mμ. 4. In the same ether solution was also found a lipid stain positive substance, changing the properties of both direct and indirect reacting bilirubins to some extent. 5. This lipid stain positive substance was supposed to combine, in a certain form, with both direct and indirect reacting bilirubins and to play an important role as a carrier in the process of ether extraction of both direct and indirect reacting bilirubins from the serum.