The oxygen reduction reaction (ORR) at proton exchange membrane fuel cell (PEMFC) cathodes requires a relatively large amount of Pt to catalyze. Our goal is to reduce the Pt loading in PEMFC cathodes using catalysts modified by metal support interactions (MSIs), an approach commonly used in heterogeneous catalysis. We illustrate the benefits of MSIs by showing that the activity of Pt is improved by supporting it on hydrous tantalum phosphate. More dramatically, oxygen reduction on Au in changed from a 2- to 4-electron reaction simply by supporting the metal on hydrous tin oxide. The changes to the catalysis of Pt and Au are attributed to electronic and chemical effects imparted by the supports.