Cellular compartments differ dramatically in their redox potentials. This translates directly into variations in the extent of disulfide bond formation within proteins, depending on their cellular localization. It has long been assumed that proteins that are present in the reducing environment of the cytosol do not possess disulfide bonds. The recent discovery of a number of cytosolic proteins that use specific and reversible disulfide bond formation as a functional switch suggests that this view needs to be revised. Oxidative stress-induced disulfide bond formation appears to be the main strategy to adjust the protein activity of the oxidative stress transcription factors Yap1 and OxyR, the molecular chaperone Hsp33, and the anti-sigma factor RsrA. This elegant and rapid regulation allows the cells to respond quickly to environmental changes that manifest themselves in the accumulation of reactive oxygen species.