With the purpose to study the combination of monomethoxybilirubindimethylester (monoether) and dimethoxy-bilirubindimethylester (diether) with serum proteins the author studied monoether and diether useing veronal buffer solution at pH 8.5 as the electrolyte and bilirubindimethylester with normal human serum solution as the control by means of paper electrophoresis; and obtained the following results. 1. As monoether and diether are both difficult to dissolve in serum, it is difficult to prepare a concentrated serum solution but all albumins combined with these two ethers. 2. When these bilirubinoids are dissolved in serum with the use of Emasol 3130, a nonionic interface activator, these ethers are dissociated from albumins and they spread out to the distance equal to γ-globulin position. In the case of crystalline bilirubin and β-carotine, the results are exactly identical. In other words, the combination of these ethers with albumins seems to be not so persistent but is a relatively mild interactioin between these different molecules. 3. In place of the serum as mentioned above, when the bilirubinoids are dissolved in γ-globulin, likewise they spread out to the same position of γ-globulin. 4. When the bilirubinoinds, with Emasol 3130, are dissolved in a sulfate buffer solution pH 7.4, these are also spread out the distance equal to the position of γ-globulin.
Namely, the reason why these bilirubinoids are distributed in the same position as of γ-globulin seems to lie in the fact that the motility of both non-ionic interface activator and γ-globulin is equal. 5. In the speed curve of the diazo reaction in the case where bilirubindimethylester, monoether, diether are dissolved in serum with non-ionic interface activator, Emasol 3130, bilirubindimethylester presents the direct form while monoether and diether the indirect form.