A water-dilutable coating agent for preparing the base layer of a multilayer coating. The coating agent contains pigments and optionally flow-control agents, thixotroping agents, fillers, organic solvents and other customary auxiliaries. The coating agent contains as a binder an aqueous polyuretane dispersion which has a polyuertane resin acid number of 5 to 70 and which as been prepared by reacting:(A) a linear polyether diol and/or polyester diol having terminal hydroxyl groups and a molecular weight of 400 to 3,000 with(B) a diisocyanate in such a molar ratio that an intermediate product is formed which has terminal isocyanate groups,(C) and reacting the intermediate product with a compound which has two groups which are reactive toward isocyanate groups and at least one group which is capable of forming an anion and which has been neutralized with a tertiary amine before the reaction, converting the second intermediate product, obtained from (A), (B) and (C) into a predominantly aqueous phase and(D) reacting the isocyanate groups which are still present with a diamine and/or polyamine having primary and/or secondary amino groups.