Pneumonias related to mechanical ventilation pose a serious diagnostic challenge and are responsible for elevated mortality. Conventional diagnostic methods are of little help. The introduction of invasive techniques such as bronchial catling via an occluded telescopic catheter (OTC) has proven to be an important advance in diagnosis and therapy. We have compared the bacteriological results obtained using OTC with those using conventional diagnostic methods such as tracheobronchial pumps (TBP) and hemocultures, and we have undertaken a bacteriological, clinical follow-up of the cases. Seventy-four patients under mechanical ventilation and suspected of pneumonia were under study. The study consisted to two consecutive phases of collecting bacteriological samples throughout the patient's evolution. A total of 121 fibrobronchoscopies were performed. The sensitivity obtained with OTC was 76%, and the specificity was 100%. The two techniques, OTC and TBP, coincided in 38% of the cases. According to the bacteriological results obtained with OTC, the antibiotic treatment was modified in 44.5% of the patients. The sensitivity of the OTC was significantly less in those patients were the last doses of antibiotic was administered within two hours of performing the procedure. The procedure of gathering secretions from the inferior respiratory tract with OTC possesses greater sensitivity and diagnostic specificity in patients with mechanical ventilation and pulmonary infiltrates and improves the diagnosis performed by other conventional and routine techniques such as TBA and hemocultures.