The main physical regularities which allow one to use a strongly charged hydrogel in purifying and/or enrichment technologies are analyzed. The proposed cyclic method is based on the two known phenomena-the salt concentration redistribution in the presence of the polyelectrolyte hydrogel and the reversible gel contraction under electric current. It is shown that in order to obtain high degrees of purification and/or concentration the salt concentration must be lower than that of the polymer. Under these conditions, there is no dependence on the nature of the salt and the cycle may be repeated several times without regeneration of the gel.