Voltammetric data for the reductive desorption of alkanethiolate monolayers from gold electrodes reveal the presence of different adsorbate binding sites. This conclusion is based on a series of characterizations of monolayers formed from butanethiol and octanethiol at annealed mica-supported gold (Au/mica) and at gold supported by both chromium-primed silicon (Au/Si) and glass (Au/glass). At Au/mica, a single wave is observed for the desorption induced by a linear voltage scan. The voltammetry at Au/Si and Au/glass is, however, comparatively more complex, as reflected by the presence of at least one additional desorption wave. Results from structural characterizations (IR and X-ray photoelectron spectroscopies and electrochemical capacitance measurements) of the monolayers formed at each type of substrate and from morphological assessments (X-ray diffraction, underpotential metal deposition, and scanning tunneling microscopy) of the underlying substrates reveal that the differences in the voltammetry originate from differences in the microscopic roughnesses of the two types of substrates. Importantly, the morphological data indicate that the bulk of the gold films on all three supports has a pronounced (111) crystallinity, that the surface at Au/Mica is strongly (111) terraced, but that the surfaces at Au/Si and Au/glass have a much higher density of steps. The voltammetry at Au/mica, therefore, represents desorption from sites at Au(111) terraces. On the contrary, the voltammetry at Au/glass or Au/Si reflects desorption from both terrace and step sites with the adsorbates at step sites bound by as much as 25 kJ mol(-1) more strongly than at terrace sites. The implications of our findings for descriptions of the nucleation and growth of these systems are discussed.