Abstract A new bifunctional chelating agent (BCA), 3-(4-isothiocyanatobenzyl) triethylenetetraaminehexaacetic acid (9), has been synthesized in fast and easy conditions. An improved synthesis of its position isomer 1-(4-isothiocyanatobenzyl) triethylenetetraaminehexaacetic acid (19) is also described. Stability in serum media of the two corresponding aminobenzyl derivatives-samarium-153 complexes, respectively, 3-(4- ...