The electronic structure of 4-hydroxy-thiophenol (HTP) adsorbed on poly-Ag(100) and on NaCl(100) was investigated with photoelectron (UPS) and electron energy loss spectroscopy (EELS), supplemented by DFT/B3LYP and restricted CIS-calculations of isolated molecules in order to identify molecular emissions and characteristic losses. Whereas on NaCl(100) the HTP molecules interact mainly via van der Waals interaction, on Ag(100) a strong level shift of 0.6 eV to lower binding energies of the thiol emission was found, indicating the formation of an Ag-S bond. As concluded from intensity ratios of various emissions both in UPS and in EELS, the HTP molecule on NaCl(100) adsorbs essentially in a planar geometry, whereas on Ag(100) the angle between the HTP molecular plane and the surface is around 70degrees, in agreement with expectations from orbital symmetry and overlap. (C) 2003 American Institute of Physics.