Abstract Model experiments were carried out on the reaction behaviour of benzene, phenol and phenylalanine during chlorination with NaOCI in aqueous solution. The influence of the pH-value, concentration, reaction time and UV-light were also determined. These experiments were conducted under conditions similar to chlorination of water and the reaction products were identified by capillary GC and GC/MS. All chlorinated isomers of benzene including HCB, formed by chlorination of benzene, were identified and quantified. However, monochlorobenzene was the major reaction product (in μg/I-concentrations). The chlorinated organic substances formed by the reaction of phenol with NaOCI were determined quantitatively. Phenylalanine/NaOCI reaction lead to the formation of 22 chlorinated organic compounds. Thirteen of these were identified and quantified. Under the influence of UV-light, the reaction of benzene/NaOCI formed primarily higher chlorinated propane derivatives, chlorinated phenols and octachlorocyclohexandiene derivatives. Similar results were obtained with the reaction of phenol/NaOCI and the phenylalanine/NaOCI. The formation of chloroform during all these reactions were determined quantitatively.