The flow conditions and solution concentrations used in the investigation were similar to those present in practical electrodialysis cells. The concentration of hydroxyl ions which appeared on the receiving side of the polarizing anion selective membrane was measured as a function of current density. The important finding was the large effect traces of dissolved organic matter in the feed water had on the onset and concentration of alkali produced in the receiving stream. For unpoisoned membranes an value of 4000 amp cm equiv−1 was obtained. This is an order of magnitude greater than reported in previous studies.