Fifty-eight flexible fiberoptic bronchoscopies were performed in 49 immunocompromised patients in the diagnostic evaluation of pulmonary infiltrates. Transbronchial lung biopsy (TBB) provided a specific diagnosis in only 12 of 47 procedures (26%). The addition of bronchial brushings to the procedures slightly increased the diagnostic yield. The yield of bronchial brushings was enhanced in patients with diffuse infiltrates on chest roentgenogram (P less than 0.05). Nonspecific inflammatory or fibrotic changes were the most common histologic finding on TBB when pulmonary parenchyma was obtained (found in 16 of 47 procedures, or 34%). Alternative specific etiologic diagnoses were established in 7 of these 16 cases by other diagnostic modalities. Contrary to previous reports, further evaluation of nonspecific changes on TBB may lead to changes in therapy and improved prognosis in selected patients. Complications related to the bronchoscopic procedures were infrequent and resulted in no prolonged morbidity.