The reaction rate, the catalyst potential, the catalyst work function and the voltammetric charge have been in situ measured during a galvanostatic transient of ethylene combustion on an IrO2 catalyst at 380 degreesC. It was found that the catalytic activity of an IrO2 catalyst could be increased by electrochemical pretreatment. In situ catalyst work function measurements showed that after the electrochemical pretreatment the IrO2 catalyst has a higher work function. Cyclic voltammetry measurements have shown that there is a linear relation between the voltammetric charge and the rate of ethylene combustion. The activation of the catalyst was explained through the formation of a higher oxide in a two-stage mechanism.