One hundred fifty-one transtracheal aspirates (TTA) from 134 patients with suspected bronchopulmonary infection were cultured aerobically and anaerobically. Transtracheal aspirate cultures contained fewer pathogens than did cultures of expectorated sputum. The diagnosis of bronchopulmonary infection caused by anaerobic bacteria could only have been established bacteriologically by transtracheal aspiration. Gram stain of TTA provided prompt and accurate bacteriologic diagnosis in more than 90% of instances, while Gram stains of expectorated sputum were nonspecific. Side effects of transtracheal aspiration included subcutaneous emphysema, hemoptysis, and a respiratory arrest in one patient. In this series, transtracheal aspiration was relatively safe and productive of valuable data that provided early diagnosis in patients with suspected bronchopulmonary infections.