The mechanism of electrooxidation of methane at 25 degreesC in 0.5 M HClO4 on the noble metal electrodes Pt, Au, Pd, Ru and Rh has been investigated by 'in situ' infrared spectroscopy. The final product of oxidation was found to be CO, in all cases. Using the technique of surface enhanced infrared absorption spectroscopy and deuterated water solutions, it has been possible to detect the presence of adsorbed intermediates such as CO and -CHO (or -COOH) for the first time. The infrared signal enhancement observed could be accounted for by considering the increase in the surface area of the electrodeposited metals as indicated by the cyclic voltammograms. Pt and Ru appear to have the highest, and Au the lowest, electrocatalytic activity among the metals studied.