In U.S. patients with the acquired immunodeficiency syndrome (AIDS), Pneumocystis carinii pneumonia is the most frequent AIDS-defining opportunistic infection. Sputum induction and bronchoscopy are effective techniques for obtaining specimens used to identify P. carinii although debate continues over their optimal use, specifically whether to perform bronchoscopy after a negative induced sputum examination for P. carinii. To evaluate the usefulness of bronchoscopy in this situation, we reviewed all cases of suspected P. carinii pneumonia in which sputum induction for P. carinii was performed at San Francisco General Hospital during a 4-yr period. Bronchoscopy, performed after a negative induced sputum examination, yielded a diagnosis in 50.5% of evaluations. The most frequent diagnoses were P. carinii pneumonia (192), tracheobronchial Kaposi's sarcoma (93), tuberculosis (28), and Cryptococcus neoformans pneumonia (9). Bronchoscopy provided either the only or an earlier diagnosis in 64.3% of tuberculosis cases. Bronchoscopy with BAL was free of complications, and, importantly, a negative BAL examination for P. carinii allowed physicians to discontinue empiric P. carinii pneumonia treatment in 95%. In patients with suspected P. carinii pneumonia with a negative induced sputum examination for P. carinii, early bronchoscopy with BAL should be performed.