Effects of grinding media and electrochemical conditions on selective flotation of copper and zinc were investigated using three different complex sulphide ore samples. Grinding medium had a strong effect on the electrode potentials and the flotation results of the three ore types studied. Copper recovery increased by 80% within a narrow potential range in the flotation of the Pyhasalmi ore that represented an "easy" ore type whereas only 15% increase in copper recovery occurred in the flotation of the "difficult" Aljustrel ore. The "moderate" Grong ore responded to the potential as with the Pyhasalmi ore but the potential for complete depression of copper was 100 mV lower. The optimum potential range of the chalcopyrite electrode was +50 to +150 mV (vs. SHE) in the copper flotation of the complex sulphide ore types studied. The optimum potential of the sphalerite composite electrode in the zinc flotation of the three ore types was that obtained using full aeration. The Aljustrel and the Grong ores resulted in the highest Zn grades, using low potential (-150 mV) at the activation stage, whereas the Pyhasalmi ore yielded the best recovery and grade at "air set" potentials.