The adsorption of monovalent tetrabutylammonium cations and bivalent bipyridinium cations diquat and paraquat on AgI has been studied as a function of surface charge density in 0.1 M indifferent (1-1) electrolyte. Adsorption results are analyzed according to the Frumkin-Fowler-Guggenheim isotherm. The model allows analysis of the several chemical and electrostatic free enthalpy contributions both to the lateral and to the adsorbent-adsorbate interactions. Hydrophobic interactions are shown to be the major non-Coulombic driving force for adsorption. The influence of adsorbate valency is consistently accounted for by the model.