A method for pretreating a copper surface for the subsequent formation of a firmly adhesive bond between the copper surface and a plastic material substrate. The method comprises bringing a copper surface into contact with: a) hydrogen peroxide; b) an acid; c) a nitrogen-containing, five-membered, heterocyclic compound; and d) a lactam, amide, or polyamide, connected at one or more of its nitrogen atoms with at least one residue of formula (I), wherein: n is an integer from 1 to 100; R1 is hydrogen or a hydrocarbon residue with 1 to 6 carbon atoms; R2 is hydrogen or a hydrocarbon residue with 1 to 6 carbon atoms; and each R1 and R2 in a —(CHR1—CHR2—O)— moiety is selected independently of each R1 and R2 in another —(CHR1—CHR2—O)— moiety.