Copper electrodeposition on to a platinum substrate from an acid sulphate plating bath was investigated with and without the additive benzotriazole (BTAH). In voltammetric experiments, the deposition process is shifted to more negative potentials in the presence of BTAH than in its absence from the bath. Moreover, the current density of the deposition process was higher in the presence of this additive than in its absence. With or without the additive, copper deposition showed features of nucleation in the voltammetric curves. Scanning electronic microscopy (SEM) images showed that copper deposits laid down in the presence of BTAH, for any potential and charge density studied, were smoother than in the absence of this additive. X-ray spectra indicated that the electrodeposits produced in the absence or presence of BTAH were composed of a mixture of copper, copper oxide and platinum oxide and also indicated that in the presence of BTAH, the deposit was less crystalline than in its absence.