[en] Rapid separation of rare earths by cation-exchange chromatography was studied with the use of a coulometric detector. Sulfonated polystyrene resins of 8, 10, and 12% cross-linkage were used with lactate solution as eluents. The elution of rare earths was very much affected by the pH of the eluent. The results indicate that the pH-gradient elution in effective for rapid separation. Good separation was achieved by the pH-gradient elution of initial pH 3.4 and final pH 5.0. The elution of rare earths was accelerated with the addition of sodium chloride to the eluent. Some heavy metals which interfere under ordinary conditions were mostly eliminated by controlling the sodium chloride concentration of the eluent. Concentrations higher than 0.1M of sodium chloride decrease the column efficiency. The raise of temperature improves the column efficiency and the increase of cross-linkage improves the separation factor between Y and Dy. Taking into account of these results, it was possible to separate 16 rare earths (Sc and Y included) in less than 80 min. with the use of strong cation-exchange resin of particle size (8--11) μm and of a steep pH-gradient lactate solution method. (auth.)