The adsorption of P-32 labelled phosphoric acid, S-35 labelled sulphuric acid and Cl-36 labelled hydrochloric acid from 2 x 10(-2) mol dm(-3) HClO4 supporting electrode was studied at rhodized electrodes (roughness factor values about 150) by a coupled electrochemical and radiotracer technique. A special attempt is made to avoid the problems caused by the reduction of ions. It has been stated that the adsorption behaviour of H2PO4- and HSO4-(SO42-) ions is very similar and the potential dependence of the adsorption can be described by a simple relationship reported previously (G. Horanyi and E.M. Rizmayer, J. Electroanal. Chem., 198 (1986) 379; 201 (1986) 187), while the relationship for Cl- ions can be conceived as composed of at least two simple functions describing the adsorption of HSO4-(SO42-) ions, with two different sets of parameters.