Several new substituted nitroguanidines were prepared by the reaction of amines with N-methyl-N-nitroso-N′-nitroguanidine. N-γ-Nitroxybutyl-N′-nitroguanidine was cyclized to 1-nitro-2-amino-6-methyl-Δ2-tetrahydropyrimidinium nitrate by refluxing in water.