Maintaining the intracellular environment is important for the survival and proliferation of eukaryotic cells. How a cell regulates its redox potential during fluctuations in the generation of intracellular reactive oxygen species and exposure to extracellular oxidants is unclear. The recent findings that Signal Transducer and Activator of Transcription 3 (STAT3) regulates mitochondrial respiration and can be oxidised directly by peroxide to form multimers may have revealed features of a homeostatic mechanism coupling cell cycle progression to the intracellular redox potential.