Aminoplastic resin dispersions which are stable to sedimentation are obtained by condensation of aldehydes with aminoplastic resin formers in an aqueous medium, in the presence of water-soluble compounds of the formulaR--X--(A--O).sub.m --B--NHCONH--Y].sub.nhaving the substituent meanings mentioned in the description. The condensation is preferably carried out in the presence of dyestuffs or optical brighteners which have groups capable of condensation. The dispersions obtained thereby are particularly suitable for whitening the coating compositions used in the paper industry, and for coating paper, wood, films and textile materials.