The results of cultures from bronchial lavage (BL) were compared with those obtained with a telescoping protected brush catheter (PBC) in 56 nonselected patients presenting with a pulmonary infiltrate of unknown etiology. At the time of bronchoscopy, 34 patients were under antibiotics. In 20 cases, the cultures from PBC and/or BL were positive. On the basis of quantitative bacteriological analysis and medical chart review, we conclude that PBC is more sensitive and more specific than BL for the diagnosis of clinically significant infections of the lower respiratory tract.