Altering the redox state of cysteine residues on protein surfaces is an important response to environmental challenges. While ageing and fasting alter many redox processes, the role of cysteine residues is uncertain. To address this we used a redox proteomic technique, Oxidative Isotope Coded Affinity TAgs (OxICAT), to assess cysteine residue redox changes in Drosophila melanogaster during ageing and fasting. This approach enabled us to simultaneously identify and quantify the redox state of several hundred cysteine residues in vivo.