The effect of bromide and irreversibly adsorbed iodide ions on the anodic oxidation of methanol residue chemisorbed on platinized platinum has been investigated. It is shown that irreversibly adsorbed iodide ions poison the surface by blocking a fraction of the available platinum sites and that this “poisoning” has no effect on the mechanism of the anodic oxidation process. This behaviour is in marked contrast to that of chloride and bromide ions, and is attributed to the strong chemisorption of iodide ions on platinum. It is also shown that the experimental rate equations for the anodic oxidation process in acid sulfate and acid chloride solutions include a function of the type, θ M (1-θ M ), indicating a virtual independence of the heat of adsorption of the methanol residue with coverage. The observed effect has been explained on the basis of the induced heterogeneity model of the platinum surface taken together with lateral interactions between the chemisorbed species.