A scanning tunneling microscope was used to perform inelastic electron tunneling spectroscopy on single Cu(II) etioporphyrin-I molecules. The resulting vibrational spectra showed an increase in ac tunneling conductance at 359 mV. This change was attributed to the vibrational excitation of the methene bridge C-H stretch mode. Vibrational microscopy was used to image the spatial distribution of the inelastic tunneling channels involved in this excitation.