The present invention relates to a process for the production of water- and solvent-resistant coatings by coating substrates with an aqueous coating composition containing as binder a mixture of(1) reaction products, containing anionic structural units of the formula ##STR1## in a quantity of 5 to 1200 milliequivalents per 100 g of said reaction products, obtained by reacting organic polyisocyanates with salts of cyanamide and bases selected from ammonia, volatile primary and secondary amines having a pKb-value of at least 3.1 and any volatile aliphatic tertiary amines and(2) polyepoxides having at least two epoxide groups per molecule and an epoxide equivalent of at least about 80, said polyepoxides being used in a quantity corresponding to an equivalent ratio of epoxide groups to anionic structural units of about 0.1:1 to 3:1, andcross-linking the binder at a temperature of about 5 to 200.degree. C. The present invention is also directed to the aqueous coating composition based on components 1 and 2.