The adsorption of 1-hydroxybenzotriazole (BTAOH) on the copper electrode was studied by surface-enhanced Raman scattering spectroscopy (SERS) as a function of electrode potential and pH value of the solution. A striking similarity between the SERS spectra of BTAOH and the respective spectra of benzotriazole (BTAH) was observed in spite of significant differences in the normal Raman spectra of these compounds. A hypothesis assuming transformation of the BTAOH molecule into BTAH at the copper surface has been verified by H/D isotopic exchange experiments. The unique sensitivity of the SERS spectrum to isotopic exchange found in acidic medium (pH 2) at considerably negative electrode potentials together with some differences between the SERS spectra of BTAOH and BTAH indicated that BTAOH is mainly adsorbed in its molecular form. However, the transformation from the adsorbed BTAOH molecule to the surface complex of BTA(-) anion with Cu(I) was suggested for alkaline solutions and potentials more positive than -0.2 V. (C) 2004 Elsevier B.V. All rights reserved.