The present invention relates to a process for manufacturing a sheet of paper and/or board from a fibrous suspension, according to which, before the formation of said sheet, added to the fibrous suspension, at one or more injection points, are at least two retention aids respectively: (a) at least one water-soluble organic cationic polymer P1 having a cationicity greater than 2 meq.g- 1 , and (b) at least one water-soluble amphoteric polymer P2 of at least one anionic monomer and of at least one cationic monomer. The polymer P2 is added to the fibrous suspension after dissolving, in aqueous solution, the polymer P2 previously obtained by one of the following polymerization techniques: - gel polymerization, suspension polymerization, inverse emulsion polymerization, dispersion polymerization. The polymer P2 has a factor F > 2, said factor F being defined by the formula: F=UL² x [(100-A)/(100-C)] with UL: Brookfield viscosity of the polymer P2 at 0.1% by weight in a 1M aqueous solution of NaCl, at 23°C, with a UL module and at 60 rev.min-1, A and C corresponding respectively to the molar percentages of the anionic and cationic monomers of the polymer P2.
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