The reduction of electrodeposited manganese dioxide (EMD), birnessite, and Bi-birnessite electrodes was investigated using a constant-current intermittent discharge technique under conditions where major kinetic effects had been minimized. The results suggested that each type of manganese dioxide underwent a homogeneous reduction followed by a heterogeneous reduction stage. The transition between these reaction mechanisms occurred at a composition that was dependent on the manganese dioxide used. The homogeneous reduction of each electrode was a complex process involving the reduction of Mn4+ ions within the various manganese dioxide structures. The heterogeneous reduction of the electrodeposited manganese dioxide and Bi-birnessite electrodes resulted in formation of Mn(OH)(2), whereas heterogeneous reduction of the birnessite electrode resulted in formation of Mn3O4.