A facile process for the conversion of N-(β-nitraminoethyl)-N′-substituted-N″-nitroguanidines into the reactive N-(β-chloroethyl)-N′-substituted-N″-nitroguanidines has been developed. N-(β-Nitraminoethyl)-N′-phenyl-N″-nitroguanidine on standing in concentrated hydrochloric acid solution gives a mixture of N-(β-chloroethyl)-N′-phenyl-N″-nitroguanidine and 1-nitro-2-phenylamino-2-imidazoline. N-(β-Chloroethyl)-N′-diethyl-N″-nitroguanidine, which is prepared in a similar manner, is unstable at room temperature and it slowly cyclizes to give 1-nitro-2-diethylamino-2-imidazoline. Some new nitroguanidine derivatives formed from the reaction of amines with methylnitrosonitroguanidine also are described.