['ARDS is life-threatening acute respiratory failure, and pneumonia is one of the most common causes of direct ARDS. Procalcitonin (PCT) has been evaluated for its utility in determining the aetiology of community-acquired pneumonia (CAP), choice of antibiotics and prediction of outcome. This study evaluated the role of PCT in predicting the outcome of patients with ARDS caused by severe CAP.', 'This was a prospective observational study conducted from September 2002 to December 2003. The plasma PCT was analysed at baseline, 24 and 72 h after enrolment and measured by ELISA.', 'Of the 22 patients with ARDS caused by CAP and enrolled in the study, 17 (77.3%) were alive 14 days after admission and five (22.7%) had died. The survivors had lower APACHE II scores (22.2 +/- 4.6 vs 30.6 +/- 9.6, P = 0.031), pneumonia severity index (141.9 +/- 2.2 vs 195.6 +/- 23.8, P = 0.005) and lower plasma PCT at baseline (9.83 +/- 3.54 vs 106.70 +/- 67.86, P = 0.004), at 24 h (10.51 +/- 5.39 vs 81.32 +/- 57.68, P = 0.014) and at 72 h (2.03 +/- 0.76 vs 19.57 +/- 6.67, P = 0.005).'] Is procalcitonin a valuable prognostic marker in ARDS caused by community-acquired pneumonia?