The rates of the acetate-catalysed hydrolyses of ten aryl acetates have been measured in aqueous solution at 25°. Nucleophilic and general base catalysis were quantitatively distinguished by a technique involving analysis of the acetanilide produced as a result of trapping the acetic anhydride intermediate by reaction with added aniline. The results confirm the dependence of the preferred mechanism on the stability of the leaving phenoxide group.