As is well known, phenol and its homologues and many of the substances containing phenolic (OH) groups generally, are much used as disinfectants. Recently it has been found that treatment of such a substance with gaseous chlorine in most cases greatly increases its bactericidal efficiency, the Rideal-Walker coefficient being definitely increased, and this is found to be so with the commercial mixture of xylenols obtained as a gas-works by-product, but to what particular compounds this is due is unknown. There is no record of any of the chloro-xylenols having been prepared by direct chlorination, though several bromo-xylenols have been made by the direct action of the reagent on the xylenols dissolved in some solvent, usually glacial acetic acid. The object of this investigation was, therefore, to study the direct chlorination of the xylenols and to isolate the mono-chloro-xylenols formed in the first stage of chlorination of certain of the xylenols, and of the commercial mixture of crude xylenols obtained in gas-works practices