Process for the preparation of di- and polyamines of the diphenylmethane series, in which a) aniline and formaldehyde are converted in the absence of an acidic catalyst to a reaction mixture comprising aminal and water, where the formaldehyde to be used comprises at most 2.0% by mass of methanol; b) water is removed at least in part from the reaction mixture obtained in step a), giving an organic phase comprising the aminal; c) the organic aminal-comprising phase obtained in step b) is converted in the presence of an acidic catalyst, giving a reaction mixture comprising di- and polyamines of the diphenylmethane series; d) the reaction mixture comprising di- and polyamines of the diphenylmethane series obtained in step c) is neutralized and then subjected to a work-up involving washing and distillation; characterized in that in step a) at least one auxiliary reagent from at least one of the groups (i) to (ii) or at least one auxiliary reagent from exclusively group (iii) is added in the mass fractions stated in each case, the mass fractions referring to the total mass of all of the feed substances used in step a) including the mass of the auxiliary reagents added: (i) 0.0001% by mass to 3.0% by mass of alkali metal halides, (ii) 0.0001% by mass to 0.030% by mass of alkali metal hydroxides, (iii) 0.1% by mass to 3.0% by mass of cycloaliphatic alcohols having 5 to 7 carbon atoms, where the mass fraction of the auxiliary reagent of group (iii) is selected such that this is greater than 0.5% by mass, based on the total mass of the aniline used in step a) and of the auxiliary reagent of group (iii). a) aniline and formaldehyde are converted in the absence of an acidic catalyst to a reaction mixture comprising aminal and water, where the formaldehyde to be used comprises at most 2.0% by mass of methanol; b) water is removed at least in part from the reaction mixture obtained in step a), giving an organic phase comprising the aminal; c) the organic aminal-comprising phase obtained in step b) is converted in the presence of an acidic catalyst, giving a reaction mixture comprising di- and polyamines of the diphenylmethane series; d) the reaction mixture comprising di- and polyamines of the diphenylmethane series obtained in step c) is neutralized and then subjected to a work-up involving washing and distillation; characterized in that in step a) at least one auxiliary reagent from at least one of the groups (i) to (ii) or at least one auxiliary reagent from exclusively group (iii) is added in the mass fractions stated in each case, the mass fractions referring to the total mass of all of the feed substances used in step a) including the mass of the auxiliary reagents added: (i) 0.0001% by mass to 3.0% by mass of alkali metal halides, (ii) 0.0001% by mass to 0.030% by mass of alkali metal hydroxides, (iii) 0.1% by mass to 3.0% by mass of cycloaliphatic alcohols having 5 to 7 carbon atoms, where the mass fraction of the auxiliary reagent of group (iii) is selected such that this is greater than 0.5% by mass, based on the total mass of the aniline used in step a) and of the auxiliary reagent of group (iii). (i) 0.0001% by mass to 3.0% by mass of alkali metal halides, (ii) 0.0001% by mass to 0.030% by mass of alkali metal hydroxides, (iii) 0.1% by mass to 3.0% by mass of cycloaliphatic alcohols having 5 to 7 carbon atoms, where the mass fraction of the auxiliary reagent of group (iii) is selected such that this is greater than 0.5% by mass, based on the total mass of the aniline used in step a) and of the auxiliary reagent of group (iii).