Procalcitonin, a new innovative inflammation parameter is presently being evaluated in clinical studies. It has been shown to be increased markedly in patients with severe bacteria induced inflammation, septic shock, endotoxinaemia and multiple organ failure. In contrast, severe viral infections or inflammatory reactions of non-infectious origin as well as auto-immune or allergic disorders do not or only very moderately increase procalcitonin serum levels. Because procalcitonin is observed at significantly higher concentrations in bacterial infections, it might assist differentiation between these infections and other aetiologies of critical illnesses. Furthermore, procalcitonin correlates with the severity of infection and sepsis and thus could serve as a useful marker for monitoring surgical high risk patients. Procalcitonin may serve as a valid and sensitive indicator for bacterial infection with important diagnostic potential in the peri-operative period and in intensive care medicine.