Temporal oscillations in the Belousov-Zhabotinsky (BZ) reaction catalyzed by RU(bpy)(3)(2+) show complex behavior with the variation of light intensity, which originates from an additional Br- flux from either inorganic or organic reactions of the BZ mechanism. As a first task, the reaction of the inorganic part of the ruthenium-catalyzed BZ reaction was investigated under illumination of the system in the visible range. The concentrations of Br- and Ru(bpy)(3)(3+) were measured simultaneously by using a bromide ion-selective electrode in a spectrophotometric cell at different initial concentrations. The role of oxygen in this procedure was examined and found to be responsible for the evolution of Br-, rather than a direct reduction of bromate by the catalyst in the excited state. Mechanistic suggestions are made to explain these photoinduced effects.