The electrochemical behavior of MnO2 electrodes during cathodic reduction in buffered medium ( 1MKOH ) was studied on the basis of diffusion of protons into the solid phase according to Coleman's theory. The kinetics of the process was followed by means of a diffusion equation which predicts the general form of the discharge satisfactorily during potentiostatic and galvanostatic reductions. A method for determining the product of the active surface area of the electrode by the square root of the diffusion coefficient of protons in the crystal lattice is given and results are compared for various samples of MnO2 .