Studies of the -SH group effect present in dithiothreitol (DTE) with respect to morphology and electrode kinetics of copper electrodeposits on the (1 1 1) plane of a copper single crystal and polycrystalline copper from highly purified solutions of acidified copper sulphate were made. At 2.0 and 5.0 mA cm−2 there was a truncation of pyramids to layers and ridges and then to polycrystalline growth with an increase in the concentration of DTE in the bath. At higher current densities the change was from pyramids to thin hexagonal blocks, dragged pyramids and then to polycrystalline growth. Interestingly, the above morphological changes repeated at two different concentrations of DTE corresponding to two -SH groups present in the molecule. Levelling of the grains was observed at all current densities studied on a polycrystalline substrate. The electrode kinetic parameters have been correlated with the morphological changes and transport mechanisms have been proposed for different concentrations of the additive.