The growth of silver on reconstructed and unreconstructed Pt{1 0 0} has been investigated using low energy electron diffraction (LEED), Auger electron spectroscopy (AES) and cyclic voltammetry (CV). In agreement with earlier studies, the underpotential deposition (upd) of silver gave rise to two adsorption states, one corresponding to the first silver monolayer (0.43 V versus Ag+ \ Ag) and the other associated with completion of a second monolayer (0.02 V versus Ag+ \ Ag) in which the electrovalencies of Ag were estimated to be I and 0.77, respectively. However, in addition, it was found that the peak intensities derived from each of these adsorption sites were a sensitive function of the underlying surface morphology. That is, a more disordered silver deposit was formed when upd occurred onto Pt{1 0 0}-hex relative to the (I x 1) phase. The on-set of oxide formation at less positive potentials was also a characteristic of the more disordered silver phase. These results are in accordance with previous investigations of copper and palladium growth on reconstructed and unreconstructed Pt{1 0 0}. It is also demonstrated that the upd peak at 0.43 V versus Ag+ \ Ag corresponds to incomplete stripping of the silver monolayer, the residual first monolayer of silver forming an oxide phase which could be detected after immersion using AES analysis as reported also by Wieckowski and coworkers (Surf. Sci. 335 (1995) 44) for silver upd on Pt{1 1 1}. Another striking feature of the Ag/Pt{1 0 0} electrochemical system was its propensity to form surface alloys after repetitive potential cycles as reported previously by Aberdam et al. (Surf. Sci. 239 (1990) 71). However, for a defect-free Pt{1 0 0}-(1 x 1) surface no alloy formation took place. It is concluded that step and kink sites are a necessary prerequisite for alloying to proceed at an appreciable rate and that each of these defects generates a Ag-Pt alloy of differing surface composition. Evaporated films of silver prepared in UHV on reconstructed and Pt{1 0 0}-(I x 1) surfaces each gave rise to Stranski-Krastanov growth. LEED revealed that the hex reconstruction was completely lifted after one monolayer of silver had been deposited. No overlayer superstructures other than (I x 1) were observed in the range of silver coverages studied (theta(Ag) < 5 monolayers). (C) 2003 Elsevier B.V. All rights reserved.