The kinetics of the hydrogen oxidation reaction (HOR) were measured at high surface-area platinum/Vulcan carbon (Pt/VC) films before and after exposure to aqueous solutions of either sodium sulfide (Na2S) or mercaptopropionic acid (MPA, HSCH2CH2COOH) using rotating disk electrode (RDE) voltammetry. At 45-90% blocking of surface Pt atoms by inorganic sulfur, sulfur appears to adsorb as oligomerized sulfur (S-n). Current-potential RDE data for the HOR at Na2S-exposed Pt/VC films were fitted to a recently developed dual-pathway kinetics model. At a submonolayer Sn coverage of surface Pt atoms, the exchange current densities for the potential-independent Tafel-Volmer pathway, or two-site HOR pathway, decrease by about 10-50-fold compared to electrochemically cleaned Pt/VC films. Exchange current densities for the single-site, potential-dependent Heyrovsky-Volmer pathway decrease by comparable factors at the same levels of sulfur exposure. The potential-range constant gamma increases in the presence of adsorbed S-n. The exposure of Pt/VC to aqueous solutions of MPA, an organosulfur species, results in similarly diminished HOR exchange current densities at Pt/VC, as observed for Na2S exposure, but yields higher values of gamma. The model is sufficiently sensitive to delineate the effects of different catalyst poisons on HOR kinetics at carbon-supported nanoscopic Pt. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3211946] All rights reserved.