A possible diagnostic role of procalcitonin (PCT) as a marker for ventilator associated pneumonia (VAP) in patients with an already triggered acute phase response after successful cardiopulmonary resuscitation (CPR) was investigated. In 28 patients with return of spontaneous circulation (ROSC) after out of hospital CPR, measurements of PCT, C-reactive protein (CrP), white blood cell count (WBC) and body temperature were compared with the clinical course of the patients. In this setting, PCT was the only marker to differentiate between patients with and without VAP (median value on day 1, 6.0 vs. 0.5 ng/ml; P<0.001). Using a cut off value of 1 ng/ml during the first 7 days after ROSC PCT had a sensitivity of 100% and a specificity of 75% to indicate VAP. PCT was elevated a median of 2 days earlier than the clinical diagnosis of VAP. Elevations in PCT can, therefore, indicate bacterial complications in cardiac arrest patients with a non-infectious acute phase response.