 The study is undertaken as prospective, randomized, controlled, multicenter trial. The study population, ICU patients with empiric antibiotic treatment due to suspected but unproven infection, is randomly assigned to either a Standard Care Group or a Procalcitonin PCT Guided Group. In the standard care group, antibiotic treatment would be based totally on clinical decision making with traditional thought processes i.e., cultures, response to antibiotics, risk of untreated infection, other laboratory findings, etc.. The PCT guided group will use the same traditional thought processes and in addition the physician will be given access to a PCT value for Day 1 and Day 4 along with the recommended thresholds for likelihood of infection. In conjunction with other laboratory findings and clinical assessments the threshold of PCT is used to continue or discontinue empiric antibiotic treatment. 