Release of fugitive organic vapors into a nuclear air cleaning system was found to result in significant lowering of the efficiency of silver zeolite filters for adsorption of iodomethane. Apparent regeneration was achieved on samples of the media through thermal desorption of poisons. Analysis showed alkylbenzenes to be the desorbed material. This was correlated with use of solvent-based materials in the contained area; potential for such poisoning reactions was confirmed from published studies of π complexes of silver.