ObjectiveTo assess the usefulness of the telescoping plugged catheter in the diagnosis of nosocomial pneumonia. DesignProspective study. PatientsA total of 103 ventilated patients with suspected pneumonia were prospectively studied over 20 months. ResultsThe quantitative cultures of the protected brush specimen detected pulmonary bacterial infection (>103 cfu/mL) in 49 (47.5%) patients. Subsequent follow-up confirmed pneumonia in 41 patients; in only one patient was a positive protected brush specimen culture established as a false-positive result. There were 54 patients with <103 cfu/mL and the diagnosis was excluded in 36 of them. We identified eight patients with false-negative protected brush specimen cultures. The results obtained by this technique allowed us to modify treatment in 49 (47.5%) patients. ConclusionsThe telescoping plugged catheter demonstrated significant bacterial infection in a relatively small proportion of patients in whom bacterial lung infection was suspected. This technique can be safely performed and is a sensitive and specific method to establish the cause of pneumonia, thus allowing specific treatment and the avoidance of inappropriate antibiotic therapy. (Crit Care Med 1991; 19:171)