Cyclic voltammetry and in situ FTIR spectroscopy have been employed to characterize NO adlayers at platinum and rhodium single-crystal electrodes. These adlayers, which are generated upon surface decomposition of nitrous acid, give infrared spectra similar to those observed for the same surface at high NO coverages under UHV conditions. The N-O stretching frequency turned out to be potential dependent with a significant upward shift as the electrode potential increased. The analysis of the absolute spectra obtained for NO-covered Pt(lll) and Rh(lll) electrodes shows a linear variation of the band center frequency of linearly bonded NO with slopes of 65 and 20 cm(-1) V-1, respectively. In addition to this potential dependence of the N-O stretching frequency, the spectra obtained with the Rh(lll) electrode suggests the existence of a change from bridge to linearly bonded NO as the electrode potential increases. Parallel voltammetric experiments allowed the determination of the surface coverage.