The electrodeposition of Cu-Co multilayers was investigated in the presence of two additives, sodium dodecylsulfate (SDS) and saccharin. Cyclic voltammetry, steady-state polarization, impedance spectroscopy, and potential pulses were carried out using an electrochemical quartz crystal microbalance. Magnetoresistance measurements were performed on Cu-Co multilayers deposited on indium tin oxide g-lass. Saccharin strongly inhibits the discharge of cobalt whereas SDS has a depolarizing effect. However the reaction path is not markedly changed. The deposition of cobalt starts with a strong evolution of hydrogen due to diffusion-controlled reduction of protons. The giant magnetoresistance ratio is markedly reduced by these additives.