Forty-eight patients underwent flexible fiberoptic bronchoscopic examination under fluoroscopic guidance, with biopsy and brushing of an endoscopically invisible primary cancer of the lung. A diagnostic (abnormal) specimen was obtained by biopsy of brushing (or both) in 29 patients (60 percent), by biopsy alone in 22 (46 percent), and by brushing alone in 19 (40 percent). Success in obtaining diagnostic tissue was related to cellular type, location by bronchopulmonary segment, size of the tumor, and distance of the tumor from the hilum.