Abstract: The present invention relates to a process for preparing di- and polyamines of the diphenyl methane series. More specifically, the process comprises reacting aniline and formaldehyde by (1a) mixing aniline with hydrochloric acid to form aniline hydrochloride, and (1b) mixing the aniline hydrochloride with a first portion of aqueous formaldehyde; or (1c) mixing aniline with a first portion of aqueous formaldehyde to form an aminal, and (1d) mixing the aminal with hydrochloric acid; to obtain a first reaction product; (2) converting the first reaction product to a second reaction product comprising di- and polyamines of the diphenyl methane series in a cascade of 4 to 25 reaction zones arranged in series, wherein a second portion of aqueous formaldehyde is added to the second of the reaction zones, in which second reaction zone the temperature is equal to or up to 20° C.