The degree of oxidation during grinding and its effect on galena flotation were studied using a specialised mill which permitted chemical conditions during grinding to be controlled. It was found that iron oxidation species derived from the grinding medium played a dominant role in galena flotation. The amount of hydroxide consumed to maintain the grinding pH at a constant value depended on the production of iron oxidation species. Linear relationships were obtained between the amount of hydroxide consumed to maintain a constant grinding pH and the production of iron oxidation species as well as galena recovery. These relationships should eventually permit oxidation during grinding and galena flotation to be predicted. (C) 2002 Elsevier Science Ltd. All rights reserved.