Developing chemical sensors with pronounced sensitivity towards lanthanides is a very important task related to the analytical control of industrial processes in nuclear industry. Various diamides of organic acids were shown to be very effective for such sensing applications when employed as ligands in plasticized polymeric membranes of potentiometric sensors. The chemical structures of some of these ligands (diamides of diglycolic acid) are very similar to those suggested in 80’s as Ca(II) ionophores that were later commercialized. We have hypothesized that commercial ionophores ETH 129 (N,N,N′,N′-tetra[cyclohexyl] diglycolic acid diamide) and ETH 5234 (N,N-dicyclohexyl-N′,N′-dioctadecyl-diglycolic diamide) originally intended for calcium detection can provide noticeable potentiometric sensitivity towards lanthanides. To confirm this hypothesis a series of PVC-plasticized sensor membranes containing ETH 129 and ETH 5234 were prepared. The sensing properties of these membranes in aqueous solutions of rare earth metals were studied and compared to earlier developed lanthanide sensors based on diamide ligands. It was found that commercial calcium ionophores indeed provide pronounced sensitivities towards lanthanides, scandium, and yttrium, while the selectivities in presence of calcium ions are in the favor of Ca(II).