Abstract: The invention relates to aqueous dispersions based on a polyurethane synthetic resin which has been obtained by reacting a hydroxyl-containing unsaturated polyester with a diisocyanate and reacting the product with a dihydroxycarboxylic acid, dihydroxysulfonic acid, diaminocarboxylic acid or diaminosulfonic acid, neutralizing the intermediate product with a tertiary amine and transferring it into an aqueous phase, and then reacting the terminal isocyanate groups with a primary and/or secondary diamine, as a chain-lengthening agent. The dispersions contain hydrolyzed shellac as second binder component. They produce coatings having excellent solvent resistance and excellent adhesion, even to difficult substrates.