Definitions for the terms of “SIRS”, “sepsis”, “severe sepsis” or “septic shock” have been proposed by the ACCP/SCCM Consensus Conference in 1992, and are now widely used. Systemic inflammatory response syndrome (SIRS) encompasses a variety of complex findings that result from systemic activation of the innate immune response. The clinical parameters include two or more the following: Fever (>38° C) or hypothermia (<36° C), increased heart rate (>90 beats/min), tachypnea (>20 breaths/min) or hyperventilation (PaCO2 < 32 mmHg), and altered white blood cell count (>12,000 cells/mm3 or <4000 cells/mm3) or presence of >10% immature neutrophils. Traditional markers of systemic inflammation, such as CRP, erythrocyte sedimentation rate (ESR) and white blood cell count (WBC), also have proven to be of limited utility in such patients due to their poor sensitivity and specificity for bacterial infection. Early diagnosis and appropriate therapy of sepsis is a daily challenge in intensive care units (ICUs) despite the advances in critical care medicine. Procalcitonin (PCT); an innovative laboratory marker, has been recently proven valuable worldwide in this regard.