Abstract: Cellular response of wild type S. cerevisiae and the Deltayfh1 mutant to oxidative stress (OS) was examined by stressing cells through the addition of H₂O₂ to the growth medium. The Deltayfh1 mutant is unusual in that it accumulates iron in it's mitochondria. Wild type growth was immediately arrested and recovered in 2 hrs following H₂O₂ treatment. No change in viability was observed. Growth of the mutant on the other hand was similar to wild type yeast for 4 hrs but then rapidly declined, eventually reaching zero. Levels of carbonyl groups and reactive oxygen species (ROS) reached their maximum at 3 hrs following exposure. The impact of OS on protein function was also evaluated by proteomic techniques targeting protein carbonylation. Oxidized proteins were selected by affinity chromatography and following trypsin digestion peptide fragments were identified by RPLC-MS/MS. A total of 53 proteins were identified in both wild type and mutant cells, respectively.