The interaction of benzotriazole (BTAH) with the surface of a corroding copper-nickel alloy in a sulfide polluted salt solution reveals a change in its role from an inhibitor to a promoter of localized corrosion as its concentration changes. A concentration of BTAH >= 5 x 10(-4) M inhibits the corrosion reaction in both the polluted and the unpolluted media. On the other hand, a concentration of 10(-4) M BTAH promotes the localized corrosion of the alloy in the polluted medium while it acts as an inhibitor in the unpolluted salt solution. This finding is substantiated by measurements of mass loss and current transients and examination of the surface by SEM microscopy. (C) 2008 Elsevier B.V. All rights reserved.