Abstract: Chlor-alkali cells of the membrane type are highly susceptible to multivalent metallic impurities in the brine feeds. As the impurity concentration builds up on and/or in the membrane material, cell voltage increases and current efficiency is lost. By the practice of the instant invention the membrane is rejuvenated and the current efficiency of the cell increased by intermittently replacing the normal brine feed thereto with a brine which is of relatively high purity with respect to the multivalent metallic impurities found in the normal brine feed. Generally, the pure brine feed should have little or no hardness (calcium and magnesium level) or, if present, the hardness should be completely complexed by a phosphate treatment. The other multivalent metallic impurities should be present in the "pure" brine at less than 2 milligrams per liter in total and preferably less than 1 milligram per liter thereof, while each individual other metallic contaminant should not exceed 0.