Reduction of cytochrome c and 2,6-dichloroindophenol was observed on iodide-modified colloidal silver films. Two different processes were identified : reduction at sub-to monolayer coverages by I- on the Ag surface and reduction in the presence of free iodide in solution. In the former, only about 5% of the electron acceptor molecules relative to surface-bound I- underwent reduction, whereas in the latter a 1:1 stoichiometry was observed. Emission around 425 nm indicated the formation of molecular silver iodide. It was concluded that, in the absence of an electron acceptor, binding of iodide to the silver surface forms a complex which is different from molecular AgI. The electron derived from partial charge transfer between I- and the Ag metal resides near the silver-iodide complex and does not contribute to the ＇free＇ electron density of the silver nanoparticles.