2,3-Diaminophenazine is the product from the horseradish peroxidase-catalyzed oxidation of o-phenylenediamine.

NMR and mass spectroscopic evidence has been obtained which indicates that the product of the oxidation of o-phenylenediamine by hydrogen peroxide, uncatalyzed or catalyzed by horseradish peroxidase, is 2,3-diaminophenazine. These results settle disparate literature descriptions. The process is most likely free radical in nature starting with the abstraction of a labile amino hydrogen atom.