The kinetics of the oxidation of some representative organic sulphoxides (to the corresponding sulphones) by potassium t-butyl peroxide in toluene have been studied in the presence of crown polyethers. A two-step reaction mechanism involving preliminary nucleophilic attack by the peroxide on the sulphoxide, followed by the breakdown of the reactive intermediate thus formed via heterolysis of the O–O bond is envisaged. Addition of the protic species ButOH and PriOH in large excess over the reactants depresses the rates. However, with initial concentrations of Ph2SO and ButOOK of ca. 5 × 10–2 and 0.5 × 10–2 M, respectively, addition of up to ca. 10–2 M-ButOH is observed to enhance the rate. On changing the alcohol from ButOH to PriOH, and the substrate from Ph2SO to (p-MeOC6H4)2SO, to Me2SO, the variation k2,obs. with alcohol concentration follows a trend which depends on the nature of the alcohol and on structure of the sulphoxide. This yields useful information on the reaction mechanism.