A series of 2,6-diamino-4-tertiary-amino-pyridine 1-oxides is disclosed. Substituents in the 4-position include diethylamino, pyrrolidinyl, piperidino, morpholino, thiomorpholino, and N-methylpiperazino. Novel oxadiazolones such as 5-amino-7-(1-piperidinyl)-2H-[1,2,4]-oxadiazolo[2,3-a]pyridine-2-one which are useful in the preparation of the pyridine 1-oxides are also disclosed. The compounds of this invention lower blood pressure in normotensive and hypertensive mammals and are particularly useful in the treatment of hypertensive conditions in mammals. 2,6-Diamino-4-(1-piperidinyl)pyridine 1-oxide is a representative embodiment of the invention.