The effect of sulphide addition to the corrosion of copper in 3% NaCl was studied. The concentration of sulphide was remained rather low, up to 10 ppm. The effect of sulphide to copper corrosion is controversial in the literature and worth to verify by means of various experimental techniques. The polarization curves, plotted from a potential close to the open circuit one to negative or to positive direction indicated a decrease of corrosion current density, explained in the literature by the protective effect of CuS. In contrast, a quartz crystal microbalance, with electro-deposited copper indicated the increase of corrosion rate with increasing sulphide ion concentration. The EIS measurements showed also an acceleration of corrosion rate by addition of sulphide ions in sodium chloride solution. It is concluded that the presence of sulphide ions in the seawater accelerates the corrosion of copper. To protect the copper structure from the corrosion in presence of sulphide as pollutants, the anticorrosion effect of a new molecule, 3-methyl 1,2,4-triazole 5-thione was examined. The action of this molecule results in the reduction of the both anodic and cathodic current density, and its inhibiting efficiency reached a value of 90% at the concentration of 10 mM. (c) 2007 Elsevier Ltd. All rights reserved.