The adsorption of thiourea (TU) on monocrystalline copper electrodes of basal indices: (111), (100) and (110) was studied by impedance spectroscopy and radiometry. Differential capacity of copper electrodes in 0.01 M NaClO4 solution containing TU of concentrations from 10(-6) M to 5 x 10(-4) M has been measured. The obtained electrochemical and radiometric data were analyzed to determine the surface concentration, coverage and adsorption parameters of TU as a function of electrode potential, and the bulk concentration of the adsorbate. The values of limiting surface concentration of adsorbed TU as well as the Gibbs energy of adsorption depend on the plane of Cu electrode and follow the sequence: Cu(111) > Cu(100) > Cu(110) which is in agreement with the surface density of copper atoms. (c) 2006 Elsevier B.V. All rights reserved.