Abstract: The philosophy of resolving actinon-lanthanon mixtures via cation-exchange elution with selective chelating agents is considered in view of the lanthanon chelate formation constant sequences obtained with various ligands derived from polyamino-polycarboxylic acid analogues of bis(2-amino-ethyl)ether-N N,N'N'-tetraacetic acid. Stability constant data and other characteristics of a newly synthesized variant, bis (2-aminoethyl)ether-N,N,N'-triacetic acid-N'-(3-propanoic acid) are reported. The possibility of its potential application is discussed for separation of actinon-lanthanon mixtures by ion exchange.