Peroxiredoxins are thiol proteins involved in antioxidant defense and redox signaling. One putative signaling mechanism involves the facilitated oxidation of associated proteins via a redox relay. We have investigated if removal of the cytoplasmic peroxiredoxins Prdx1 and Prdx2 influences the redox state of other thiol proteins in cultured cells. A mass spectrometric proteomic approach in which reduced thiols in one cell type were labelled with a heavy isotope tag and reduced thiols in the other cell type with a light isotope tag, was used to compare wild type (WT) Jurkat cells with cells in which either Prdx1 or Prdx2 was knocked out (KO).