Phenol was first found in normal urine by von Städeler1in 1851. Since his day the phenols isolated from urine are phenol, paracresol, orthrocresol, pyrocatechin, hydroquinone, and para-oxybenzoic acid. The most important of these, according to Baumann,2Mooser,3and Siegfried and Zimmermann,4is paracresol. Städeler tested the urine distillate qualitatively with Millon's reagent. Baumann used a gravimetric method in which he converted the phenol into crystals of tribromphenol. The first volumetric method was originated by Messinger and Vortman. This was modified by Kossler and Penny,5and later by Neuberg,6Mooser,3Siegfried and Zimmerman,7and finally by Ellinger and Henzel.8Among the colorimetric methods worthy of notice are those of Bananni,9Bordas and Bobin,9and Kiesel.9It remained, however, for Folin and Denis to devise a method which was both accurate and clinically applicable. In 1879 H. Senator,10