Electrodeposited Co-Cu/Cu multilayers have been produced with current control from a sulfate bath with and without NaCl as an additive. The addition of NaCl decreases the current efficiency of the multilayer deposition and results in multilayers with lower GMR and higher electrical resistivity than the chloride-free bath. The grain size of the deposit and the degree of orientation also decreases if the additive is present. It has been concluded that the adsorption of chloride, the formation of copper(I) intermediate, the change in the deposition mechanism, the increase in nucleation rate, and the occurrence of a non-Faradaic current transient all contribute to the enhancement of the structural disorder that leads to the loss in GMR. Some general conclusions have also been formulated about the role of additives in electrodeposition baths, especially concerning the differences in d.c. plating and pulse-plating.