1. When dihyrobilirubin is prepared from crystalline bilirubin by direct contact reduction with the use of collagenous palladium, at least over 100 mg crystalline bilirubin is required and it is necessary to saturate callagenoes palladium sufficiently with hydrogen before the use. 2. Crystal of dihydrobilirubin isolated from pyridine solution or isolateid by column chromatography, when dissolved in chloform solution, shows the absorpton peak at 437 mμ on the absorption curve. 3. In the primary elevation paper chromtography of dihydrobilirubin conducted at 20°C using Schleicher and Schüll-No.2043 filter paper when the developing agent is acetone-water-ammonia in the proportion of 80: 15.5, Rf equals 0.02; while when the combination is in the ratio of 40:50:10, Rf equals 0.10. 4. When dihydrobilirubin previously added with iodine is made to undergo Schlesinger reaction, it turns bluish green, emanating red fluorescent light, and shows the absorption peak at 630 mμ and 585 mμ on its absorption curve. 5. Oxide of dihydrobilirubin is greenish blue, and when it is dissolved in a 5% methanol hydrochloride, the absorption curve shows the peak at 675 mμ and 365 mμ. 6. When a dihydobilirubin serum solution is put to filter paper electrophoresis, it acts in combination with serum albumin.