The reduction of oxygen at clean and at adsorbate-covered silver electrodes was studied with rotating disk and rotating ring-disk electrodes. The amount of hydrogen peroxide produced on adsorbate-covered electrodes was greater than on silver electrodes in purified electrolytes of 0.05M K2SO4 and 0.1M KOH. Reducing oxygen at low pH (0.05M H2SO4) also produces a relatively large amount of hydrogen peroxide. Electrochemical evidence is given for the participation of O2 in the mechanism of oxygen reduction on silver. An electrochemical mechanism for the formation and growth of microspots in photographic emulsions is described in which the reduction of oxygen (or H2O2) is viewed as the cathodic component and the oxidation of silver as the anodic half-cell of a corrosion cell. -- AATA