Abstract Introduction: Peroxiredoxin (PRDX) and Thioredoxin (TRX) are antioxidant proteins that control cellular signalling and redox balance, although their response to exercise is unknown. This study aimed to assess key aspects of the PRDX-TRX redox cycle in response to three different modes of exercise. Methods: Healthy males (n=10, mean ± SD: age 22 ± 3 yrs) undertook three exercise trials on separate days: two steady-state cycling trials at a moderate (60% MAX; 27 min, MOD) and high (80% MAX; 20 min, HIGH) intensity, and a low volume high intensity interval training trial (10×1 min 90% MAX, LV-HIIT). Peripheral blood mononuclear cells (PBMCs) were assessed for TRX-1 and over-oxidised PRDX (isoforms I-IV) protein expression before, during and 30 minutes following exercise (post+30). The activities of TRX reductase (TRX-R) and the NF-κB p65 subunit were also assessed. Results: TRX-1 increased during exercise in all trials (MOD +84.5%; HIGH +64.1%; LV-HIIT +205.7%; p<.05), whereas over-oxidised PRDX increased during HIGH only (MOD -28.7%; HIGH +202.9%; LV-HIIT -22.7%; p<.05). TRX-R and NF-κB p65 activity increased during exercise in all trials, with the greatest response in TRX-R activity seen in HIGH (p<.05). Discussion: All trials stimulated a transient increase in TRX-1 protein expression during exercise. Only HIGH induced a transient over-oxidation of PRDX, alongside the greatest change in TRX-R activity. Future studies are needed to clarify the significance of heightened peroxide exposure during continuous high intensity exercise and the mechanisms of PRDX-regulatory control.