Cyclic voltammograms were recorded in 0.5 H2SO4 for Pd, Pt, Rh, Pd-Pt (6 at.% on surface), Pd-Rh (62 at.% on surface), Pd-Pt (60 at.% on surface) before and after 30-min adsorption of CO2, Pd-Rh (78 at.% on surface) before and after 45-min adsorption of CO, for a ternary alloy (81:6:13 at. %) Pd-Pt-Rh, and for a ternary (44:35:21 at. 0/6) Pd-Pt-Rh alloy before and after 15-min adsorption of CO. The absorption, adsorption and desorption of hydrogen was strongly inhibited by CO. Absorption of hydrogen on the Pd alloys was not affected by CO2 which was adsorbed only on the Pt and Rh surface atoms, and not on the Pd atoms. The different behavior of CO and CO2 enables the activity of individual surface centers in Pd alloys to be distinguished in the reactions involving adsorbed hydrogen. The CO and CO2 adsorption products are different. 23 refs.