The surface area of samples of manganese dioxide is shown to be an important factor in influencing its behavior. Four samples of MnO~ of widely different origins, electrolytic, activated, natural ore, and synthetic pyrolusite, with total surface area values of 52.8, 50.5, 7.4, and 1.6 mS/g, respectively, are used as examples. The rates of the recuperation reaction at temperatures of 21~ 50~ are shown to be related to the total surface area of the oxides by a complex relation, dependent on temperature and other factors. The product of the reaction MnOOH develops on the surface and in the pores of the original MnO~ particle, thus increasing the diameter and resulting in reduced pore volume, respectively. The MnOOH made under these conditions, from all four starting materials, appears as rod-shaped units in electron micrographs.