A method is developed for electrophoretic fractionation of serum proteins in agar gel with simultaneous specific sorption of gamma-globulin fraction, migrating during the electrophoresis through specific immunosorbents incorporated into agar gel. The reaction was carried out in a special apparatus designed for the electrophoresis in two perpendicular directions. The sorbent was separated from impurities by passing the current in the first direction. The unspecific sorbent did not alter the electrophoretic mobility of migrating proteins, but the specific sorbents immobilized completely both antibodies and antigens. The antibodies were shown to bind repeatedly to the immunoglobulins, which had been linked to the sorbent. The method facilitated distinctly the estimation of antigens and antibodies in complicated mixtures. By analogy with affinity chromatography a term 'affinity electrophoresis' was used for designation of the method described.