Known methods and devices for pre-treatment of electrically conducting and non-conducting substrates require a relatively high level of technical outlay and are difficult to incorporate into the following coating process. Pre-treatment frequently does not ensure the adhesion required for coating. The invention proposes to maintain a low pressure glow discharge between the substrate to be cleaned and a counter-electrode. The substrate is periodically alternately switched as a cathode or anode, the frequency of the alternation being set in the range of from 1 Hz to 1000 Hz and the pulse lengths and/or the discharge voltage being independently adjustable. The method is used as a preliminary process for the coating of substrates which require an adhesive layer. Cutting tools, in particular, made of steel, hard metal or ceramic are treated before being coated.