Abstract: Organic higher functional polyisocyanates are obtained by separating a mixture containing isomers of diphenylmethane diisocyanate and higher functional polyisocyanates having more than two benzene rings. The mixture is distilled under vacuum at a pressure of between 10.sup.-3 and 10.sup.-1 mm/Hg. under conditions which avoid chemical change in the organic polyisocyanates contained in the mixture. The polyisocyanates are separated into two fractions with a desired first fraction containing said higher functional polyisocyanates with only a trace of the isomers which is less than about 6% of the weight of the first fraction and having a viscosity of more than 10,000 cp/25.degree. C. The second fraction consists essentially of said isomers and can be further purified by crystallization.