A series of mono- and diazaphenothiazines have been synthesized. The oxidation potentials of these compounds have bee[n] determined and discussed. The ESR spectra for the free radical form of these compounds have been recorded and discussed. The relative stabilities of the free radical form of these ring systems in concentrated sulfuric acid have been reported. The synthesis of 2-hydrazino-3,4-diazaphenothiazine and 3,4-diazaphenothiazine have been reported for the first time.