Aqueous polyester imide dispersions are prepared by allowing molten polyester imide to solidify and then comminuting it in the dry state to a particle size of 100 .mu.m or less, whereupon the particles are milled in water to a particle size of less than 5 .mu.um. The dispersions may be used for the manufacture of heat-resistant bonds and impregnations and for electrical insulation of metallic conductors. m.