The interaction of poly(ethylene glycol) M(n) = 3000 with copper I and II ions in aqueous-acidic media was studied by investigation of the specific electrical conductivity, optical density and the cyclic voltamperometric curves in Cu+ and Cu2+ solutions. The results suggest the formation of complexes of the {Cu+(-EO-)(3 .)(x - 1)H2O} and {Cu2+(-EO-)(4 .)(y - 1)(H2O)(2)}types. In the case when {-CH2CH2-O-}(n) and Cl- are simultaneously present in the copper electrolyte, the possibility of simultaneous complex formation between both copper ions and ethylene oxide units, and copper ions and chloride ions is considered. The strong increase in copper electrodeposition overpotential after the addition of polyethers to the electrolytes containing brighteners is explained by the formation of these complexes.