The amidation reaction of linear and crosslinked sulfopropyl dextran with protic and dipolar aprotic amidic solvents such as formamide, N,N-dimethylformamide, N,N-dimethylacetamide and hexamethylphosphoramide, at mild temperature, was studied. The composition of the final products can be adjusted by molar ratios. of reagents, temperature and duration of reaction. The final products are water-soluble or highly water-swellable hydrogels which possess an ion-exchange ability due to their content of unreacted sulfonic acid groups. Some physico-chemical characteristics of these new polymers are pointed out.