The author observed on the demonstrative method of propentdyopent as the differential method between stercobilin and urobilin IX, α by W. Stich and put forward the use of photometric observation with the propentdyopent reaction for the identification of propentdyopent. And the results of it's use were as follows. 1. Standing for one hour at 37°C. after the addition of 3% H(2)O(2) in 1/5 dosis of material, then standing for two hours at 37°C. after the addition of Mn O(2), the formation of propentdyopent was observed, and it displayed the absorption maximum at 315 mμ and the absorption maximum of the coloured solution by the pentdyopent reaction displayed at 518 mμ. 2. It was recognized that the value of log T 580/T 520 showed the formation of propentdyopent, i.e. the contained dosis of mesobilirubinogen, on the occasion of positive Ehrlich's aldehydo reaction, employing the above method to human urine.