Peroxiredoxins (Prxs) are a family of peroxidases that maintain thiol homeostasis by catalyzing the reduction of organic hydroperoxides, H2O2, and peroxynitrite. Eukaryotic 2-Cys-Prxs, also referred to as typical Prxs, can be inactivated by oxidation of the catalytic cysteine to sulfinic acid, which may regulate the intracellular messenger function of H2O2. A small redox protein, sulfiredoxin (Srx), has been shown to reduce sulfinylated 2-Cys-Prxs and thus to regenerate active 2-Cys-Prxs. We previously reported that cytokine-induced nitric oxide (NO) intervenes in this pathway by decreasing the level of 2-Cys overoxidation and by upregulating Srx through the activation of the transcription factor nuclear factor erythroid 2-related factor (Nrf2). Here, we describe the methods used to monitor the interplay between NO and H2O2 in the regulation of the Prx/Srx system in immunostimulated macrophages, which produce both reactive oxygen species and NO.