Procalcitonin is a glycoprotein that selectively increases in bacterial infections, sepsis and multiple organ failures. On the other hand, in viral infections, autoimmun infections or operative trauma procalcitonin level does not increase or only slightly increases. Therefore, procalcitonin can be used as a diagnostic parameter in bacterial and nonbacterial infections and as a prognostic parameter in motinorization of critical patients. The literature related to PCT was discused in the study.