Abstract: The invention relates to a method for the marking of materials with coded microparticies, wherein coded microparticles which are obtainable by (i) polymerization of at least one water-soluble monoethylenically unsaturated monomer in the presence of at least one ethylenically unsaturated monomer having at least two double bonds in the molecule by inverse water-in-oil suspension polymerization, doped nanoparticles being used as the suspending medium, (ii) emulsion polymerization of water-insoluble monoethylenically unsaturated monomers with from 0 to 10% by weight, based on the monomer mixture, of at least one ethylenically unsaturated monomer having at least two double bonds in the molecule, doped nanopartices being used as an emulsifier for stabilizing the disperse phase, (iii) polymerization of at least one ethylenically unsaturated monomer together with a copolymerizable dye which has an ethylenically unsaturated double bond, and, if appropriate, agglomeration of these partices or (iv) agglomeration of at