In making metabolism studies in cases of dementia praecox I was struck by the appearance of a red color in the urines which had been treated with strong mineral acids. The red substance was found to be insoluble in ether, chloroform, benzene, toluene and xylene, but soluble in water, ethyl alcohol and amyl alcohol. In amyl alcohol the red substance gave an absorption spectral band between 556 and 570. This compound with these characteristics seems to be identical with the urorosein described by Nencki and Sieber,1 H. Rosin,2 C. A. Herter,3 J. Ph. Staal,4 L. C. Willard,5 V. Arnold6 and A. Ellinger and A. Flammond.7 According to the work of Herter, the urorosein is formed from indol-acetic acid by the action of a strong mineral acid and an oxidizing agent. That indol-acetic acid is derived from tryptophan can hardly be doubted,