A simple continuous-flow method is described for the determination of sulphite (0.30–3.0 µg ml–1) based on the chemiluminescence produced by cerium(IV) reduction. The emission intensity is greatly enhanced by the presence of 3-cyclohexylaminopropanesulphonic acid, which acts as a sensitiser. The analysis is automated, requires no sample pre-treatment and samples can be analysed at a rate of 50 h–1 with a relative error of about 2%. The method was applied satisfactorily to the determination of sulphur dioxide in air.