The electrochemical response of adsorbates produced on polycrystalline Pt from thiourea, methyl thiourea, 1,3 dimethyl thiourea and tetramethyl thiourea dissolved in aqueous 0.5 M sulfuric acid are comparatively studied using electrochemical routines. The adsorption kinetics of thioureas on Pt follows an Elovich-type equation. Their saturation coverage, measured from the decrease in the H-atom electrosorption charge after correction for molecular size for steric effects, decreases as the size of the molecule producing adsorbates increases. Adsorption data fulfill the empirical Frumkin isotherm with a repulsive adsorbate–adsorbate lateral interaction term. Adsorbate electrooxidation starts at about 0.65 V vs SHE. The deprotonation of hydrogen-containing thioureas yields soluble products, their electrochemical behaviour being to some extent similar to that of formamidine disulfide. For E > 0.65 V vs SHE, the oxidation of thioureas can be described as complex processes in which intermediates compete with oxide layer formation on platinum.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas