N-Amination of 6-amino-2-methyl-4-pyrimidone with O-(mesitylenesulfonyl)hydroxylamine leads to the 3-amino derivative. The isomeric 1,6-diamino-2-methyl-4-pyrimidone was obtained by the N-amination of the O-benzoyl derivative of the initial pyrimidone and removal of the benzoyl protection.