Ascorbate and several phenolic compounds readily oxidise in cell culture media to generate hydrogen peroxide. However, media containing pyruvate showed much less H2O2 production, apparently because pyruvate can scavenge H2O2 in the medium. Researchers must be aware that compounds under test can sometimes readily oxidise in cell culture media, that this might not be detected by measurement of H2O2 if the media contain pyruvate, and that pyruvate can be substantially depleted in the media as a result. (C) 2009 Elsevier Inc. All rights reserved.