Examination of Benzotriazole-treated surfaces on copper, and the complexes produced when benzotriazole and analogous compounds react with cuprous and cupric ions in an aqueous solution, has shown that the film produced on copper has a polymeric structure and is chemically bonded to the metal or metal-oxide surface. Thickness of the surface film is less than 50 Ã…, which complicates elucidation of the film structure. Exploratory work, therefore, has been based upon examination of the copper-benzotriazole complexes produced by precipitation in solution and it has been shown that the complexes also contain water molecules or hydroxyl ions, and that their structures are modified when other anions are present. Other nitrogen-containing heterocyclics also form polymeric complexes with copper, both on the metal surface and in the solution, but do not exhibit the strong inhibitor properties of benzotriazole. Benzotriazole is effective for most copper-base materials and affords protection in aqueous and gaseous environments polluted with sulpher dioxide, hydrogen sulphide and salt mist. Benzotriazole can be applied as an aqueous solution or be incorporated into lacquers and polishes. A particularly valuable method of application is to expose the metal component to benzotriazole-inpregnated paper. -- CAL