Chlorination and thermal degradation of 2-chlorodibenzodioxin and dibenzofuran were investigated using sealed tubes at 350°C in the presence of CuCl 2 or CuCl. Twelve organic species, including polychlorobenzenes, were identified and quantified as a function of residence time. Time behaviours of PCDDs and PCDFs regarding destruction processes were compared. The formation of polychlorobenzenes from the thermal heterogenous degradation of PCDDs was only a minor pathway but it could contribute to the good linear correlation observed between the concentration of polychlorobenzenes and those of PCDD/Fs in the emissions of municipal solid waste incinerators.