Water-soluble, nitrogen-containing condensates are prepared by reacting a cross-linking agent, obtained by(a) condensing 1 mole of a dicarboxylic acid of 4 to 10 carbon atoms with from 1 to 2 moles of a polyalkylenepolyamine, having 3-10 basic nitrogen atoms in the molecule, to give a polyamidoamine and(b) reacting the polyamidoamine with epichlorohydrin and/or dichlorohydrin in aqueous solution at a pH of from 4.5 to 8.5 and at below 100.degree. C., from 1 to 130 parts by weight of epichlorohydrin and/or dichlorohydrin being employed per 100 parts by weight of the polyamidoamine from (a),with ammonia, a primary amine, a polyamine containing 2 to 4 N atoms, a polyether-amine or a polyamidoamine in aqueous solution at below 100.degree. C.The condensates are used as retention aids, flocculants and drainage aids in papermaking.