The accuracy of morphologic diagnosis from transbronchial fine needle aspirates (TBN), bronchial secretions (BS), bronchial washings (BW), brush biopsy (BB) and forceps biopsy (FB) sampled via a flexible fiberoptic bronchoscope, was studied in 60 malignant lung tumours. In visible tumours the best results were obtained with FB (85%) while TBN was positive in 65%. In cases were bronchoscopy only showed secondary signs of tumour, the sensitivity of FB, BB and TBN was higher than that of BW and aspiration of BS. In tumours not visible through the bronchoscope, the diagnostic accuracy of BB, BW and aspiration of BS was higher than that of FB and TBN. In the diagnosis of carcinoma of the lung the diagnostic accuracy of combining FB and one cytologic method (BW) was higher than that of any of the single methods (p less than 0.05) while no appreciable increase was achieved by using additional methods.