Ventilator-associated pneumonia (VAP), a bacterial infection that develops after 48 hours or more of intubation, is associated with high morbidity and mortality. Rapid identification of VAP is required to improve survival and to reduce avoidable treatment-associated side effects. Procalcitonin (ProCT), a blood test, is a reasonably specific marker of bacterial infection and its level increases early in sepsis. In this study, a ProCT serum level will be measured in 50 patients with clinically suspected VAP. We aim to show that the ProCT level will be high early in VAP and will stay high in patients with poor prognosis. This will help to address the potential role of ProCT as part of early diagnosis and management of VAP.