Abstract: An improved process for the preparation of methylene-bridged polyphenylpolyamine mixtures having increased 4,4'-isomer content in the diaminodiphenylmethane portion by the catalyzed condensation reaction of aniline and formaldehyde is disclosed. Aniline and formaldehyde are mixed and reacted at an elevated temperature in the presence of up to about 3 weight percent of a co-catalyst system comprising about 0.1 to less than about 3.0 weight percent silica-alumina catalyst and from about 0.1 to less than about 3.0 weight percent oxalic acid, basis weight of aniline present. The novel process provides a resulting reaction product that can be easily filtered to remove the solid silica-alumina catalyst therefrom and a reaction product mixture of methylene-bridged polyphenylpolyamine mixtures having an increased 4,4'-isomer content in the diaminodiphenylmethane portion than heretofore obtained utilizing silica-alumina catalysts alone.