Although fiberoptic bronchoscopy (FOB) has been traditionally used to evaluate nonresolving pneumonia, its efficacy is unknown. We, therefore, reviewed FOB in 35 consecutive patients who had (1) a roentgenographic infiltrate, (2) cough, (3) either temperature greater than 38.1 degrees C, leukocytosis, sputum production, (4) symptoms present for at least ten days, and antibiotic therapy for at least one week. Known lung cancer and AIDS were excluded. Fiberoptic bronchoscopy was diagnostic in 86 percent (12/14) in whom a specific cause was found. No patient had endobronchial cancer. Two patients with nondiagnostic FOB and persistent systemic symptoms had open lung biopsy specimens showing Wegener's granulomatosis and bronchiolitis obliterans with organizing pneumonia (BOOP). Twenty-one patients with nondiagnostic FOB had no final diagnoses other than community-acquired pneumonia. We conclude that FOB is extremely useful in finding a specific diagnosis for a nonresolving pneumonia when a specific diagnosis can be made. Fiberoptic bronchoscopy was most likely to yield a specific diagnosis in nonsmoking patients with multilobar infiltrates of long duration and could have been avoided in older, smoking, or otherwise compromised patients with lobar or segmental infiltrates with no decrease in diagnostic yield in our series.