The general principle involving the exchange of interlamellar cations in clays with those in its aqueous environment has been examined in the case of Langmuir-Blodgett films of metal salts of fatty acids. X-ray diffraction as well as X-ray photoelectron studies on Langmuir-Blodgett films made up by sequential deposition from two troughs containing various metal ions with the same fatty acid condensed Langmuir monolayer have been studied. Evidence is presented for the first time of the exchange of metal ions between the interlamellar spaces of the negatively charged fatty acid bilayers with those in its aqueous environment.