The stability of a bilayer at or near the surface of a Langmuir-Blodgett multilayer of cadmium arachidate is investigated by fluorescence spectroscopy. Changes in the fluorescence spectrum with time, monitored over more than 200 h, indicate that rearrangement and loss of labeled molecules occurs even at room temperature in air. The nature of this change is perturbed by dipping the multilayer into the subphase an additional time, even when no further material is deposited atop the multilayer. Placing an additional bilayer of either cadmium arachidate or a polypeptide copolymer with alkyl side chains atop the labeled bilayer sharply reduces its mobility and suppresses somewhat the rate of change of structure in that bilayer. Adding a bilayer of polyglutamate affects the labeled bilayer’s lateral mobility more than does adding a bilayer of cadmium arachidate. This is due to the interdigitation of the polyglutamate’s side chains with the layer upon which it is deposited. However, addition of the cadmium arachidate bilayer is more effective in reducing sublimation.