The interaction of sulfur with Pt(111), Zn/Pt(111) and Cu/Pt(111) has been examined using X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), and thermal desorption mass spectroscopy (TDS). At temperatures between 300 and 600 K, the exposure of Pt(111) to S-2 gas produces a chemisorbed layer of sulfur without the formation of bulk sulfides. Exposure of S-2 to a Zn/Pt(111) alloy, at room temperature, results in a breakdown of the alloy and formation of a zinc-sulfide film on Pt(111). Further S-2 exposure at 550 K sulfidizes the remaining metallic zinc without affecting platinum. For the Cu/Pt(111) surface alloy, on the other hand, exposure to S-2 at 550 K leads to sulfidation of the platinum. Platinum can effectively compete for sulfur atoms bonded to copper but not for those bonded to zinc. The reaction of S-2 gas with Cu/Pt(111) surfaces produces copper sulfides that promote the sulfidation of Pt by providing surface sites for the dissociation of S-2, and by favoring the diffusion of S into the bulk of the system.