a process is described for the isolation of 4 , 4 &# 39 ;- diaminodiphenylmethane in substantially pure form from admixtures thereof with the corresponding 2 , 4 &# 39 ;- isomer and 2 , 2 &# 39 ;- isomer . the isomeric mixture of diamines is heated , optionally in the presence of an inert organic solvent , with at least two equivalents , per mole of said diamine mixture , of a phenol or bisalkylidenephenol . the 4 , 4 &# 39 ;- diaminodiphenylmethane forms a complex with said phenol and the 4 , 4 &# 39 ;- isomer of the diamine is isolated therefrom in substantially pure form by treatment with alkali or by heating to dissociate . the isomeric mixture of diamines used as starting material can be employed in the form of a mixture of polymethylene polyphenyl polyamines containing a major portion of said diamines .