The invention describes new aromatic diisocyanates having the formulas: ##STR1## in which R is an alkyl radical with 1 to 12 carbon atoms. Preferably they are 1-alkyl-2-isocyanatomethyl-4-isocyanatobenzenes and/or 1-alkyl-4-isocyanatomethyl-2-isocyanatobenzenes and, particularly, 1-methyl-2-isocyanatomethyl-4- and -6-isocyanatobenzene and/or 1-methyl-4-isocyanatomethyl-2-isocyanatobenzene. The new diisocyanates are preferably prepared by phosgenation of the corresponding diamines and subsequent thermal cleavage of the carbamic acid chlorides formed on an intermediary basis and are used for the preparation of plastics, preferably of polyurethanes, and crop protection agents.