Potential modulated reflectance spectroscopy (PMRS) has been used to study the anodic oxidation of ruthenium. Although the cyclic voltammograms of ruthenium in alkaline solutions are broad and relatively featureless, PMRS allows identification of soluble RuO42- (Ru(VI)) and RuO4- (Ru(VII)) species formed at the onset of oxygen evolution. The PMR spectra exhibit an isosbestic point that is attributed to the RuO42-/RuO4- redox couple. The peaks in the PMR spectra correlate well with reported lambda(max) values of RuO42- at 470 nm and RuO4- at 385 and 315 nm, The PMR spectra can be fitted to a difference spectrum calculated from the absorption spectra of the two species. PMR studies of ruthenium dissolution in acid solutions indicate that RuO4 is the only identifiable corrosion product formed in the oxygen evolution region in this case.