IN the course of experiments on overpotential at low current densities, during the past four years, we have frequently observed that stirring the solution affects the overpotential. Although our work is far from complete, we now have considerable evidence that, if very great precautions are taken to exclude oxygen and also any products of electrolysis arising from the anode, stirring has little or no effect on the potential of a cathode of a noble metal. For example, some time ago, using cells in which a smooth tungsten or platinum anode was separated from a gold cathode only by a sintered glass plug, stirring caused a considerable lowering of overpotential at the cathode, with polarizing currents less than about ten microamperes per sq. cm. In later work, using very great care over purity of materials and cleanliness of apparatus, and an anode of platinized platinum which could be in the same solution as the cathode, stirring did not affect the potential of cathodes of platinum or gold appreciably. The platinized anode, in the atmosphere of hydrogen, also carefully purified, reduces completely any oxygen produced at the anode, provided that the current is less than about 100 μamp./cm.2; this is confirmed by its potential remaining steady at the reversible hydrogen value. With these conditions, stirring had no effect on cathodic potential between 0.05 μamp./cm.2 and 100 μamp./cm.2.