It has been well established that an exchange transfusion is a radical therapeutic measure for prevention of "Kern Ikterus". However, side effects of massive transfusion have been reported in large number of cases and several attempts of medicamental treatment to reduce an opportunity of the exchange transfusion have also been evaluated. In this connection, effects of ACTH and Glycyrrhizin on neonatal jaundice were determined in mature infants during first 7 days of life. 1) Serum bilirubin was significantly decreased by ACTH administration, while suppression of serum bilirubin increment, characteristic changes in neonatal period, was observed following Glycyrrhizin administration. 2) ACTH administration resulted in hyperglycemia, increased urinary electrolytes, 17 KGS and bilirubin excretion. However, amounts of increased urinary bilirubin excretion was found to be one tenth of amounts of decreased serum bilirubin. On the contrast, no remarkable changes in blood sugar, electrolytes, urinary electrolytes, 17 KGS, and bilirubin excretion was noted following Glycyrrhizin administration. 3) On the treatment of hyperbilirubinemia, serum bilirubin were significantly decreased in cases of induced hyperglycemia. 4) Characteristic decrease on red blood cell counts, osmotic fragidity, Hb. and Ht. during neonatal period were improved by Glycyrrhizin, while no effect was found on reticulocyte counts. It may be summarized that ACTH has wide effects on bilirubin metabolism including a interaction of glucose metabolism and Glycyrrhizin relate a prevention of hemolysis increasing osmotic fragidity of red blood cell. Therefor, it may be emphasized that ACTH may be used for the treatment of neonatal hyperbilirubinemia, while Glycyrrhizin may be expected for the prevention of neonatal hyperbilirubinemia.