The contribution of the bronchial aspirate and postbronchoscopic sputum toward the establishment of a correct diagnosis of bronchogenic carcinoma was evaluated. A total of 273 patients underwent diagnostic bronchoscopic procedures during a 27-month period. One hundred four of these 273 patients were eventually found to have bronchogenic carcinoma. The combination of biopsies by forceps and brushings yielded the diagnosis in 61 (97 percent) of 63 endoscopically visible tumors. Neither bronchial aspirates nor postbronchoscopic specimens of sputum produced an additional diagnosis. The same combination yielded a diagnosis in 17 (41 percent) of 41 endoscopically nonvisible tumors. In these endoscopically nonvisible tumors, unlike tumors, a combination of bronchial aspirates and postbronchoscopic specimens of sputum produced a total of eight additional diagnosis. Thus, the overall diagnosis of endoscopically nonvisible tumors was improved from 41 percent (17/41) to 61 percent (25/41). Both bronchial aspirates and postbronchoscopic specimens of sputum were therefore important sources of diagnosis in endoscopically nonvisible tumors.