Among the six Prx isoforms in mammals, Prx4 emerges as the most attractive, easily accessible biomarker candidate as it was initially designated as a secretable peroxidase [2,9], has recently been identified in the circulation of healthy and diseased individuals [10,11] and, finally, has been linked to morbidity and mortality in patients with sepsis in the intensive care unit and patients with non-specific complaints in the emergency department [12,13]. The gene discussed is PRDX4; the disease is Sepsis.