It has been shown that nitroguanidine, nitriminoimidazolidine, and 1-benzyl-2-nitriminoimidazolidine behave like urea by formation of potassium salts which completely hydrolyze in water. By contrast to true primary nitramines with which they might be considered to be tautomeric, the nitrimines are classed like urea as practically neutral compounds. Despite this ostensible tautomerism which was formerly evoked to explain the survival of nitroguanidine and nitriminoimidazolidine in alkaline solution it is now believed that the salts of nitroguanidine and nitraminoimidazolidine, from which the original nitrimines are regenerated upon acidification, are not intermediates, but rather end products, in the slow reaction with alkali. The intermediate is now postulated as an hydroxyisonitraminate anion from which the several products of the reaction are formed by appropriate fission. Presumably this anionic intermediate also is operative when tetraethylnitroguanidine or 1,3-dibenzyl-2-nitriminoimidazolidine is converted by alkali into tetraethylurea and 1,3-dibenzyl-2-inuclazolidine respectively.