The reaction of the CO oxidation over a Pt-Rh heterophase surface, which represents 10-20 nm platinum particles located on a rhodium film, which in turn is deposited on an inert support, has been investigated at low pressures (P < 2x10(-5) mbar). The results are compared with the data for the clean surfaces of Pt and Rh. In the high-temperature range, the rate of CO2 formation on the heterophase surface is found to be higher than the sum of the rates on individual metals corrected by the surface area of the different metals. The nature of the synergistic effect in the. CO oxidation is discussed.