The adsorption of saccharin on Au(1 1 1) single crystal in 0.1 M HClO4 solution has been investigated by cyclic voltammetry and capacitance-potential measurements. From pH measurements, it is concluded that the deprotonated molecules form the adsorbed monolayer. The charge under the peaks and spikes present in the voltammograms is associated with a charge transfer involving deprotonation and adsorption of the organic molecules. The stability range of the adsorbed monolayer is extended by an increase in the saccharin concentration and a decrease in the temperature. Ordering of the monolayer has been proposed on the basis of the current transients associated with the formation of the monolayer. (C) 2003 Elsevier Science B.V. All rights reserved.