Macrocyclic ionophores in thin films are of interest for sensors or novel ionophotoswitching devices. Continuing work on floating monolayers and Langmuir-Blodgett mutilayers of macrocyclic ionophores-such as crown ether ionophores, cyclodextrins and valinomycin-is reviewed. The figure shows a schematic representation of the complex of valinomycin (a biopolymer based on a 36-membered ring) with potassium.