PCT No. PCT/EP97/00801 Sec. 371 Date Aug. 31, 1998 Sec. 102(e) Date Aug. 31, 1998 PCT Filed Feb. 20, 1997 PCT Pub. No. WO97/31518 PCT Pub. Date Sep. 4, 1997Partially hydrolyzed polymers of N-vinylcarboxamides obtainable by sole polymerization of N-vinylcarboxamides of the formula where R1 and R2 are each hydrogen or C1- to C6-alkyl, and elimination from the polymers of from 0.5 to 95 mol % of the groups of the formula where R1 is hydrogen or C1- to C6-alkyl, can be used as paper, paperboard and cardboard dry strength enhancers.