Sepsis is the systemic response to infection by microbial organisms. A differential diagnosis of infection caused by either bacteria or other microbial organisms is essential for effective treatment and prognostic assessment. Current clinical laboratory methods in the diagnosis of bacterial infections are either non-specific or require longer turnaround times. Procalcitonin (PCT) is a biomarker that exhibits greater specificity than other proinflammatory markers (eg, cytokines) in identifying patients with sepsis and can be used in the diagnosis of bacterial infections. In this article, we review the current knowledge of PCT and its use in the clinical laboratory setting.