Abstract: The present invention relates to a process for the preparation of aqueous dispersions of polyurethanes containing chemically fixed carboxylate and/or sulphonate groups which comprises reacting(i) isocyanate prepolymers based on organic polyhydroxyl compounds and monomeric diisocyanates, having an isocyanate content of from 1.5 to 8% by weight and containing less than 1.2% by weight of monomeric diisocyanates with(ii) organic diaminocarboxylates and/or organic diaminosulphonates and/or organic dihydroxy carboxylates and/or organic dihydroxy sulphonates and optionally other chain-lengthening agents which have hydroxy or amino groups and which are free from salt groupsin the aqueous or organic phase optionally with subsequent addition of water and optionally subsequent removal of solvent, using an equivalent ratio of isocyanate groups to amino and/or hydroxy groups in the range of from about 1:1.2 to 1:0.