The silver underpotential deposition (UPD) on thymine modified and unmodified electrodes was investigated using classical electrochemical methods combined with photoemission experiments. On unmodified electrodes positive of the Nernst potential two silver monolayers were formed. The first formed monolayer differs in its work function as well as in its 3d-band binding energy from the second monolayer/bulk material. On thymine modified electrodes only one silver monolayer is formed whereas the formation of the second monolayer is completely blocked in the UPD region. On both, the deposited silver monolayer and the bulk silver, thymine is adsorbed topmost, interacting via its N(3) atom with the surface. XPS spectra reveal an increased electron density at the N(3) in the adsorbed state compared to the signal arising from vacuum deposited thymine multilayers. The metal deposition in electrochemical environment includes two steps, firstly on the electrode adsorbed thymine has to be removed by silver ions; secondly thymine has to be readsorbed on the topmost metal layer. Therefore the influence of adsorbed thymine on metal deposition processes is strongly correlated to the energy balance between the adsorption energies of metal adatoms, thymine on the electrode and thymine on the final topmost layer. Adjusting these energies leads to the different influence of chemisorbed thymine on the formation of the first and second silver monolayer. (c) 2007 Elsevier B.V. All rights reserved.