Abstract: A method for the production of new derivatives of watersoluble cellulose ethers by the reaction of 100 parts by weight of a water-soluble cellulose ether with 3 to 30 parts by weight of C.sub.8-18 alkyl(ene) succinic acid anhydride, in the absence of water and under neutral or acid conditions at elevated temperature, until, in analytically detectable terms, 1 to 8% by weight, based on the cellulose ether, of alk(en)yl succinic acid has reacted with the cellulose molecule; the products of the method; and their use as thickners for aqueous surfactant solutions, dye dispersions, and for hydraulically setting building materials or their use as protective colloids or emulsifiers in the suspension polymerization of water-insoluble monomers in aqueous phase.