The X-ray induced irradiation damage is studied in the CH3(CH2)(11)SH monolayers on gold and platinum surfaces to get information on the metal-sulfur bonds. This is important because the sulfur-substrate bond is one of the crucial factors in thiol SAW The X-ray photoelectron spectra (XPS) of the S 2p and C 1s emission were analyzed. During the modification of the surface the thiol/platinum system behaves differently than the thiol/gold system. In the latter case the S 2p spectrum changes as a function of time during the measurement and two chemically different sulfur species, associated with Au-thiolates and irradiation induced sulfur species, can be identified in the spectra. On platinum, there are two chemically different sulfur species in pristine monolayers and their ratio remains unchanged as a function of measurement time. This trend is obviously surface induced and is related to the nature of the metal-sulfur bonds in the self-assembled thiol layers. (C) 2003 Elsevier Science B.V. All rights reserved.