The reactivity of N,N'-bis[(E)-dimethylamino)methylene]urea (1) with amines is described. Selective exchange of one of the N,N-dimethylamino fragments is possible with most of the benzylic amines tested, allowing the formation of 1-(alkylamino-methylene)-3-dimethylaminomethylene ureas as analytically pure precipitates in modest yields. Under acidic conditions, the urea fragment acts as leaving group leading the formation of symmetrical N,N'-disubstituted formamidines.