Abstract: A method for the preparation of a liquid diphenylmethane diisocyanate composition which comprises reacting one molar proportion of substantially pure 4,4'-diphenylmethane diisocyanate, as hereinbefore defined, with from 0.01 to 0.8 molar proportions of a monoalkoxy polyalkylene glycol of the formula: ##STR1## wherein R represents an alkyl group containing from 1 to 12 carbon atoms, R.sup.1 represents hydrogen or an alkyl group containing from 1 to 3 carbon atoms and n is an integer of from 2 to 58, the reaction being performed at a temperature of from 100.degree. to 250.degree. C. and in the presence of a catalyst for the NCO/OH reaction.The liquid diisocyanate compositions are useful in the manufacture of polyurethanes, especially elastomers and flexible foams.