Several phenolic compounds as well as ascorbate can oxidise in certain cell culture media (especially Dulbecco's modified Eagle's medium (DMEM)) to generate hydrogen peroxide. Addition of oxaloacetate decreased the levels of H2O2 detected and the oxaloacetate was depleted. Oxaloacetate was approximately as effective as pyruvate in decreasing H2O2 levels and more effective than alpha-ketoglutarate. Our data raise important issues to consider when interpreting the behaviour and metabolism of cells in culture (which are both altered by the oxidative stress of cell culture) and their apparent response to addition of autooxidisable compounds such as ascorbate and epigallocatechin gallate. (C) 2011 Elsevier Inc. All rights reserved.