Chemical exchange saturation transfer (CEST) agents have magnetic resonance contrast properties that can be turned on and off upon selective pre-irradiation of ¹H NMR resonances. Here we show that the CEST properties of paramagnetic lanthanide(III) macrocyclic complexes with pendent amide groups are dependent on the concentration and identity of small anionic ligands including amino acids. Data for both mononuclear and dinuclear ytterbium(III) CEST agents will be presented.