Design and Methods: All patients on mechanical ventilation for more than 48 hours and simplified CPIS ≥ 6 were enrolled prospectively. Four diagnostic procedures, endotracheal aspiration (ETA), blind bronchial sampling (BBS), blind bronchoalveolar lavage (blind BAL) and bronchoscopic BAL (BAL) were performed in same sequence within 12 hours. The bacterial density ≥ 104 cfu/ mL BAL samples were taken as reference standard.