We describe an application of the scanning electrochemical microscope that utilizes tip-sample feedback to characterize the reactivity of electro-oxidation catalysts. The kinetics of hydrogen oxidation are probed at a platinum electrode as a function of applied potential in aqueous sulfuric acid solution. Tip-sample feedback generates a tip response that reflects the rate of hydrogen oxidation at the substrate. The ability to directly measure the rate constant for hydrogen oxidation is, subsequently, used to perform reactivity mapping of heterogeneous electrodes consisting of catalytic and noncatalytic domains. Differences in reaction kinetics clearly distinguish surface composition variations based upon their reactivity toward hydrogen oxidation and illustrate the capability of this technique as a screening tool in the design of electrocatalysis. Further experiments investigating the oxidation of methanol illustrate the ability to characterize complex multistep reactions.