Results from pilot-column flotation tests on a lead-zinc ore show that it is possible to control the redox potential of the column pulp by varying the oxygen activity of the flotation gas fed to the spargers. As a result, the process chan,pes so that the fine zinc minerals are more actively floating in an oxidising environment, at the same time xanthate and frother consumptions increase. The placement of electrodes in the column does change the redox potential readings but only as a result of a change in she oxygen concentration of the pulp, However the values from a Glassy-Carbon (GC) electrode are consistently lower than those from a Pt-foil electrode at the same location. Actual positions of operating points as measured by GC-electrodes fall within the theoretical area for precipitation of lead xanthate.