With the purpose to clarify the condition of oxidation-reduction potential in the skin of jaundiced patients, the author made the preliminary experiment by the injection of 2. 3. 5. triphenyl tetrazolium chloride, neo tetrazolium chloride and blue tetrazolium into dogs and rabbits, employing the Arakawa's method, and it was recognized the T. T. C. test by Arakawa was the best method to apply to human body. Therefore, the test was attempted on 20 cases of healthy human, 110 cases of various liver and bile ducts diseases (75 cases of them showed hyperbilirubinemia over 1 mg/dl) and 21 cases of other diseases, and the above results was compared with various clinical symptoms and clinical courses. And the results were as follows. 1. Using the above agents as a oxidation-reduction. dicator of skin in living body, the sensitivity was in order of N. T C., T. T. C. and B. T., but the side effect was the most scanty in T. T. C., Therefore, the T. T. C. test by Arakawa was the best for the application to human body, and N. T. C. had the utility value on the animal experiment since the stability and sensitivity to light, but B. T. could not use. 2. The difference of oxidation-reduction potential among healty human, dog and rabbit was clearly observed, and this test was the most in rabbit, and then in dog, and the most low in human. 3. The T. T. C. test was almost negative in healthy human, but in was positive in all cases of mechanical jaundice, and it showed positive by the stadium or symptom in acute hepatitis and livercirrhosis, and it was seen at the early period of acute stadium in the former and it was seen in the cases of the latter with continuous jaundice over 60 days. In and it was negative or slight positive in chronic hepatitis. It was negative in hemolytic jaundice and others. 4. Comparing T. T. C. test with various clinical symptoms and various clinical tests, it had relation to serum total bilirubin especially direct bilirubin, alkaline phosphatase and skin itching, and it had considerable relation to serum colloidal reaction in acute hepatitis and BSP-test. 5. Therefore, it was thought that there were close correlation between the oxidationreduction potential of skin and the mechanism in which Verdinikterus was occured from the change of disposed bilirubin in skin to biliverdin.