In this multicenter, multi-national, observational study, patients admitted consecutively to the ICUs of 10 academic hospitals (8 in Canada and the United States and 2 in Europe) between 1 January 2003 and 20 November 2004 were screened for eligibility. The study protocol had been reviewed and approved by the Food and Drug Administration (protocol PCT-7; file number # I010023). Patients 18 years of age and older requiring mechanical ventilation with the new diagnosis of pneumonia within the last 48 hours were included. We excluded patients who were enrolled in a clinical study prior to baseline PCT sampling, had cardiogenic shock, had burns greater than 20% of total body surface, or were likely to die within 48 h, and postoperative patients following bone marrow transplant (within the last 6 months), coronary artery bypass grafts (within the last 7 days), and solid organ transplants (within the last 14 days). Patients were followed for 28 days after discharge from the ICU. The study was approved by local Institutional Review Boards/Ethics Committees of each participating institution and informed consent was obtained from the patients' next of kin.