A variant of counter-flow isotachophoresis of proteins on cellulose acetate membranes is proposed. The liquid counter-flow is created by electroendosmosis in the membrane. Proteins are concentrated at the Kolrausch boundary during isotachophoresis in the presence of ampholytes. The method permits one to make microanalysis of proteinic mixtures in diluted solutions, and it can be used in combination with immunodiffusion and immunoelectrophoretic methods of antigenic protein detection.