Oxidative stress refers to a systemic imbalance between oxidants, such as hydrogen peroxide, and antioxidants and is evident in many physiological perturbations (e.g. exercise) and chronic diseases (e.g. muscular dystrophies, diabetes and neurodegenerative diseases). Biomarkers of oxidative stress in blood can be used to assess the severity of oxidative stress, but the choice of the biomarker is dependent on the particular oxidant target being investigated. Thiol groups on proteins are particularly susceptible to oxidants, and one such protein, plasma albumin, containing a thiol group (cys34), has been used as a biomarker of oxidative stress. My experimental aim was to establish if there were additional proteins in plasma containing thiol groups that might provide additional information about oxidative stress in plasma. To identify thiol containing proteins, I used chemical labelling with fluorescent tags with gel electrophoresis, and stable isotopic tags with mass spectrometry. Using gel electrophoresis, thiol groups were evident on 14 protein bands. Of these, eight proteins have been identified using mass spectrometry. Data on sensitivity of these proteins, compared to plasma albumin, to various oxidants will be presented. This work provides the foundation for further investigation into the roles of thiol proteins as biomarkers in various physiological and disease conditions.