Typical urinary phenols and oestrogens have been converted into azo dyes by coupling with diazotized I.C.I. M5091. The dyes have been characterized from the following data: (a) partition properties; (b) solubility properties in a phosphate buffer; (c) adsorption properties; (d) absorption spectra data 310–600 mμ. Decalso, after treatment with barium acetate solution, has been introduced as a new adsorbent in chromatography. The removal of indigoid pigments from urinary oestriol fractions by a new procedure is described. The addition of thiourea and benzene to urines during acid hydrolysis affords some protection to oestradiol-3:17α.