The cathodic electrogeneration of hydrogen peroxide in seawater by means of oxygen reduction on a gas diffusion cathode was studied. The effects on the reaction yield of several operative parameters such as cell design, medium composition, anolyte concentration, pH and working potential were investigated. Results indicate that in a two-compartment cell notable concentrations of hydrogen peroxide are obtained with a constant yield in a wide range of charge. Lower catholyte pH values, obtainable by means of the anolyte choice, mitigate the decrease in the efficiency due to cathode fouling. Application of hydrogen peroxide electrogeneration to seawater disinfection was also tested. Comparative tests conducted using both commercial and electrogenerated hydrogen peroxide, either alone or combined with iron in Fenton's treatment, are also presented.