The use of water-soluble, amphoteric copolymers which are obtainable by copolymerization of a) at least one N-vinylcarboxamide of the general formula in which R1 and R2, independently of one another, are H or C1- to C6-alkyl, b) at least one monomer which is selected from the group consisting of (b1) monoethylenically unsaturated sulfonic acids, phosphonic acids, phosphoric acid esters and derivatives thereof, and (b2) monoethylenically unsaturated mono- and dicarboxylic acids, the salts thereof and dicarboxylic anhydrides, c) if appropriate, at least one monoethylenically unsaturated monomer differing from the components (a) and (b), and d) if appropriate, at least one compound which has at least two ethylenically unsaturated double bonds in the molecule, with the proviso that the monomer mixture comprises at least one monomer (b) having at least one free acid group and/or an acid group in salt form,and subsequent partial or complete hydrolysis of the groups —CO—R1 from the monomers (a) incorporated in the form of copolymerized units into the copolymer,as agents for increasing the initial wet web strength of paper.