Adsorption of L-alpha-lecithin (dipalmitoyl) at the water\ 1,2-dichloroethane interface has been studied by cyclic voltammetry. It has been found that the voltammetric peak in acidic medium corresponds to the desorption of the protonated form of lecithin. Its surface concentration is controlled by a surface chemical reaction of the zwitterionic form of adsorbed lecithin with hydroxonium ion. The whole process is complemented by the potential dependent adsorption/desorption equilibrium of the protonated form of lecithin. Its concentration in the organic phase is affected by the acid-base equilibrium.