Barium isotope fractionation has been observed in cation-exchange chromatography of barium salts operated in a breakthrough manner. The lighter isotopes are depleted in the front end fractions of the barium adsorption zones. Values of the single-stage separation factor minus one per unit mass difference between isotopes are 5.3 x 10(-6) for the barium chloride system, 6.1 x 10(-6) for the barium acetate system, and 4.8 x 10(-6) for the barium lactate system at 25 degrees C, No significant influence of barium-carboxylic acid complex formations on barium isotope effects has thus been observed.