We tested the effectiveness of protected bronchoalveolar lavage (PBAL), performed through a protected transbronchoscopic balloon-tipped (PBT) catheter, in collecting distal airway secretions with a minimal degree of contamination. The PBAL had less than or equal to 1% squamous epithelial cells in 91% of specimens and an absence of bacterial growth in 59% of patients without pneumonia. Using a threshold of 10(4) cfu/ml we had one false positive result in 33 patient without pneumonia and one false negative in 13 patients with pneumonia. Quantitative bacterial cultures of the PBAL specimens had a diagnostic sensitivity of 97% and a specificity of 92%, with a positive predictive value of 97% and a negative predictive value of 92%. The diagnostic efficiency was 96%. The presence of intracellular organisms in much greater than or equal to 2% of the recovered alveolar cells (Giemsa stain) was seen in all but two patients with pneumonia (on corticosteroids) and in none of the patients without pneumonia. Gram stains of the PBAL specimens were positive in all but one patient with pneumonia and negative in all but one patient without infection (patient with endobronchial narrowing secondary to neoplasm with false positive cultures). Either the Giemsa or the Gram stain was positive in all patients with pneumonia, allowing early and accurate diagnosis of lower respiratory tract infection before the results of cultures were available. The time off antibiotic therapy before bronchoscopy did not affect the result of PBAL cultures, contrary to what we observed for the protected brush specimen.