The present invention relates to a process for the preparation of di- and polyamines of the diphenylmethane series, and to the preparation of di- and poly-isocyanates of the diphenylmethane series from these di- and poly-amines. The di- and poly-amines of the diphenylmethane series are prepared by the reaction of aniline and formaldehyde in the presence of hydrochloric acid. In with the present invention, the hydrochloric acid employed contains less than 0.001 wt. % of metal ions which are divalent and/or more than divalent.