The "oxygen paradox" is that molecular oxygen is both essential for aerobic life but also can be toxic to cells largely because of the effects of oxygen-derived species collectively called "reactive oxygen species" (ROS) such as the hydroxyl radical. Cells have evolved elaborate defences against ROS but if these defences are decreased (as in ageing) or if the ROS challenge becomes too great (as in toxicity), a state of oxidative stress (OS) ensues. Proteins are the principal targets of ROS and redox proteomics uses proteomics tools to study redox-based effects on the cell's protein complement. We have long used bivalve molluscs as sentinel organisms for study of pollution effects in estuaries, in particular looking at effects on stress-response proteins such as antioxidative enzymes, detoxification enzymes and heat shock proteins. Stress-response proteins are often affected by more than one stressor so these targets are likely to be of interest in other stress contexts. We are now applying redox. proteomics approaches to study stress effects in bivalves. We detect carbonylation, glutathionylation, ubiquitination, effects on disulphide bridge patterns and changes in protein expression signatures in a range of electrophoresis formats. The effects are tissue- and treatment-specific. We find that many proteins targeted by OS are associated with either actin or protein disulphide isomerase. Many of the tools we use are species-independent and are appropriate for other stress scenarios..