The co-adsorption of chloride with thiourea and sulfate ions at a copper electrode in sulfuric acid solution has been investigated in situ by SERS spectroscopy. The presence of the halide species in solution and subsequent adsorption at the copper electrode leads to enhancement of the SERS spectra for the adsorption of thiourea and sulfate ions at the copper electrode. The in situ SERS spectra indicate that the adsorption of chloride at the copper electrode is dependent upon electrode potential and solution chloride concentration. The co-adsorption of chloride at the copper electrode in sulfuric acid electrolyte containing thiourea is particularly favoured at low potentials and is characterised by the presence of a distinct band at 300 cm(-1) which is assigned primarily to a Cu-Cl vibration. However, this band contains secondary contributions from Cu-S and Cu-O vibrations arising from the co-adsorption of thiourea and sulfate species at the copper electrode respectively.