Of 184 patients, 87 were subsequently found to have intrathoracic malignancy, 93 were found to have benign lung disease and four were lost to follow-up.CYFRA 21.1 was the most efficient marker in differentiating benign from malignant disease, with a sensitivity of 54% and a positive predictive value of 96%. Thirty seven patients who had a negative bronchoscopy subsequently turned out to have malignant disease. Either CYFRA 21.1 or CEA was elevated in 26 (70%) of such patients. Multivariate analysis showed that only CYFRA 21.1 and CEA contributed significantly to the discriminatory power of the data.We conclude that measurement of cytokeratin fragment detected by antibodies BM 19-21 and KS 19-1 and carcinoembryonic antigen at the time of bronchoscopy significantly increased the diagnostic yield in this population and was especially useful in those patients in whom tumour biopsy was not possible at bronchoscopy.