The microcalorimetric adsorption of H-2 and O-2, has been employed to probe the dispersion of metals and surface composition of the bimetallic Pd-Cu/SiO2 and Pd-Ag/SiO2 catalysts. In addition, the microcalorimetric adsorption of ethylene was carried out to study the effects of Cu and Ag on the adsorption of ethylene on reduced and oxidized Pd surfaces. It was found that the addition of Cu or Ag diluted the surface Pd sites. The heats of O-2 adsorption for Pd-Cu and Pd-Ag were approximately the averages between those for I'd and the second metal Cu and Ag, respectively, when the ratios of Cu/Pd and Ag/Pd are low (1:1). Moreover, the O/H ratio was found to be about 0.5 for the Pd-Cu/SiO2 (1:1) and Pd-Ag/SiO2 (1:1) samples, which was about the same for the Pd/SiO2 sample. These results suggest the enrichment of Pd on the surfaces in the bimetallic Pd-Cu/SiO2 (1: 1) and Pd-Ag/SiO2 (1: 1) samples. On the other hand, the initial heats of O-2 adsorption for the Pd-Cu/SiO2 (1:4) and Pd-Ag/SiO2 (1:4) are approximately equal to those of the second metal Cu and Ag, respectively, revealing the enrichment of the second metals in these samples. The addition of Cu or Ag inhibited the formation of ethylidyne on the reduced Pd surface, and Ag was found to be more effective than Cu for this effect. The adsorption of ethylene on the oxidized Pd resulted in the serious oxidation of ethylene. The addition of Cu or Ag greatly reduced the oxidation of ethylene on the oxidized Pd. In this case, Cu was more effective than Ag in reducing the activity of oxygen for the oxidation of ethylene on the Pd surface.