The copper-benzotriazole (Cu-BTA) complex which inhibits copper corrosion has been studied using x-ray photo-electron spectroscopy and electro-chemical measurements; the adsorption isotherm for BTA has been obtained. The results suggest that, at low solution concentrations, BTA is lightly adsorbed at the metal surface, while at higher concentrations a complex is formed on, or precipitated onto, the surface to give inhibition. Metal oxide already present influences film formation, and with the pH determines the valence of the copper in the Cu-BTA complex. It would seem that the cover provided by the film has more effect on inhibition than its composition does. -- AATA