CO adsorption on bimetallic Ru/Au and Ru/Cu surfaces, prepared by depositing Cu or Au on a Ru(0001) single crystal at 540 K or 1110 K, has been studied with HREELS and SSIMS. The data show that CO adsorbs on Ru/Cu surfaces in the linear coordination as is found on clean Ru(0001). On Ru/Cu surfaces the HREELS spectra for CO adsorbed at 300 K indicate a pertubation of coordination and binding energy in agreement with earlier SSIMS and TPD studies. Studies at low adsorption temperatures (120 K) show that CO adsorbs on Ru and Cu sites as well as into a new adsorption state. The data are discussed in terms of the mutual involvement of Ru and Cu in the adsorption process.