This paper describes the application of a conducting diamond film as a transparent electrode for attenuated total reflectance infrared (ATR-IR) spectroscopy during electrochemical experiments. The electrode consists of a conducting polycrystalline thin film of diamond (4-6 mum) deposited on a silicon wafer (similar to 50 mum). The electrode is pressed onto a ZnSe ATR crystal with the silicon side in contact with the crystal; electrolyte (0.5 M H2SO4) is in contact with the diamond film. We then electrochemically polarize the electrode and observe IR changes at the diamond-electrolyte interface. Before polarization, the IR spectra clearly show the presence of water and H2SO4 bands of the electrolyte. After conditioning the diamond film with cyclic voltammetry, two IR features appear in the spectra, and we have assigned to them the formation of -OH groups on the surface. One feature appears at 3240 cm(-1) (O-H stretch) and the other appears at 1100 cm(-1) (C-O stretch). These features clearly change with polarization potential, but may also depend on the amount of time spent at a critical potential. Because of their wide potential window for electrochemical reactions and their wide spectral transparency, diamond electrodes should be useful in many other spectroelectrochemical studies.