We report on an observation of electroactivity of redox-inactive proteins at liquid vertical bar liquid interface. Since except for small polypeptide protamine, using 'classic' four-electrode setup it is impossible to facilitate a transfer of proteins across liquid vertical bar liquid interface, to observe protein electroactivity a carbon electrode shielded with thin layer of organic solvent was taken. Voltammograms of such shielded electrodes are sensitive to thermodynamics of anion re-solvation. To decrease Gibbs free energy of protein transfer from water to organic phase, and, thus, to record protein electroactivity at liquid vertical bar liquid interface, the reversed micelles of surfactants able to solubilise proteins in organic solvent were formed. Varying proteins and surfactants, as well as polarity of organic solvent, we proved that the observed raise in current of shielded electrodes, which in certain cases exceeds background by the two orders of magnitude, is indeed provided by the presence of proteins. Analytical parameters of shielded electrode are dependent on protein molecular weight and its interfacial properties. Electroactivity of redox-inactive proteins registered at liquid vertical bar liquid interface gives promise for wide application of electroanalytical chemistry in proteomics. (c) 2005 Elsevier B.V. All rights reserved.