The problem of establishing an optimum procedure for the determination of the end-point of catalytic titrations was studied using computer facilities. All procedures were tested using simulated titration curves recorded in either the integral or the derivative mode. The effects of a number of factors that influence the accuracy of determination are discussed. The results were compared with those obtained by experiments in which milligram amounts of bromide and iodide were determined using a new indicator reaction, persulphate-sulphanilic acid-2,2′-bipyridine, catalysed by a small excess of silver ion. In this instance, the method of graphical extrapolation of straight portions of the integral catalytic titration curve before and after the equivalence point appeared to be the best procedure for the end-point determination.