We studied 46 patients, 26 with central visible tumors and 20 with peripheral nodules (in these, biplane fluoroscopic guidance was used), to determine the optimal number of forceps biopsies necessary to establish a diagnosis of carcinoma with the flexible fiberoptic bronchoscope. Overall yield was 96% (25 of 26) for central tumors and 75% (15 of 20) for peripheral nodules, using the combination of forceps biopsies and brushings. The combination of cytologic examinations plus one forceps biopsy produced a 92% diagnostic accuracy for central visible tumors. However, for central tumors the maximal diagnostic yield was not achieved until the fourth forceps biopsy, and for peripheral lesions accuracy continued to increase through the sixth forceps biopsy, and for peripheral lesions accuracy continued to increase through the sixth forceps biopsy in this study. Theoretically, as many as 10 biopsies may be necessary to maximize diagnostic yield for peripheral carcinomas.