Surface diffusion coefficients,DS, of platinum adatoms were measuredinsituon polycrystalline platinum electrodes inmersed in 1 M HClO4, 1 M H3PO4and 0.5 M H2SO4electrolytic solutions at different potential values. The change in theDSvalues observed, as well as the rate of change ofDSwith the potential value, confirm an adsorbate induced relaxation of Pt electrode surfaces. ©1995 American Institute of Physics.