The interaction between K+ ions and valinomycin (val) at the water/1,2-dichloroethane interface was studied using voltammetric measurements. The effect of a dibehenoylphosphatidylcholine monolayer adsorbed at the interface was also analyzed. Significant differences between the experimental transfer current and the theoretical values were found, especially for high (C-K/C-val) concentration ratios, which suggest an interfacial complexation between val and K+ ions. This process is enhanced by the monolayer due to the ability of val to penetrate into phospholipid layers. The transfer of the other alkali cations facilitated by val in the presence and in the absence of the monolayer as well as the behavior of another ligand (dibenzo-18-crown-6, db-18c-6) were analyzed for comparison. In all these cases the experimental results were the expected ones according to a facilitated transfer mechanism. The outstanding results observed for K+ transfer assisted by val are explained, taking into account the high stability constant of the K+-val complex and the surface properties of val.