Yttrium(III) equilibria in the presence of catecholamines adrenaline (AD), noradrenaline (NAD), and dopamine (DP) have been investigated by potentiometric titration in aqueous solution in I = 0.20 mol center dot dm(-3) KCl ionic medium and at 298.15 K. The complexation model for Y(III)-catecholamine systems has been established by the "BEST" software from the potentiometric data. The types of complexes in the yttrium(III)-catecholamine systems have been ascertained, and the protonation constants for catecholamines and the stability constants for yttrium(III) complexes with catecholamines have been obtained. The stability constants of YHL2+- and Y(HL)(2)(+)-type complexes are reported. Catecholamines can form stable yttrium(III) complexes with the phenolic hydroxyl groups of catecholamines as the binding site to yttrium(III). In terms of the ligands, the stability of complexes ranks in an order such as dopamine > adrenaline > noradrenaline. The stability constants of Y(III)-adrenaline complexes are higher than their La(III) complexes due to the higher ionic potential of Y(III). The ionic radii of Ca(II) and Y(III) are roughly equal, but Y(III) has a higher charge than Ca(II). Therefore, Y(III)-catecholamine complexes are relatively more stable than Ca(II)-catecholamine complexes. This result may be utilized for in vitro and in vivo studies.