The addition of 1-naphthol accelerates the photo-oxidation of alkylbenzenes when their alkyl group contains a reactive hydrogen atom.From the effects of u.v. light on dilute solutions of 1-naphthol in cumene, s-butylbenzene and t-butylbenzene, which have been floated as layers on water, it is possible to propose a mechanism by which the alkylbenzenes are oxidised under the influence of u.v. light.