The reaction of bromate with thiocyanate in dilute perchloric acid was studied potentiometrically. Experiments were carried out in a batch reactor (without feedstreams of the reactants) at a tenfold excess of bromate. Volatile compounds were permanently removed from the reaction solution by nitrogen gas bubbling at a constant flow rate. After the first large reproducible maximum, irregular oscillations appear in the time dependence of the redox. potential. An irregular evolution of gas products (probably Br-2) from the reactor also can be observed. The system is very sensitive to initial conditions as well as perturbations.