Аннотация:In course of our research of Bi(III) and Ac(III) complexes with BATA we obtained high thermodynamic stability constants as well as high stability of the complex in vivo. High stability in vivo of BiBATA is associated with the high kinetic inertness of mono- and deprotonated forms of the complex. In addition BATA was found to be superior to DOTA for the rapid chelation of Bi(III) and Ac(III) due to the less rigid structure of the 18-crown-6. Taken together it seems that the 18-crown-6 macrocycle is more preferable for such large cations as Bi(III) and Ac(III).