Summary80 cases with blocked bronchi, demonstrated bronchographically, have been reviewed. A high degree of association with bronchogenic carcinoma has been demonstrated but, contrary to the findings of other workers, bronchial occlusion due to non‐neoplastic causes was relatively frequent. In the present series a blocked bronchus was due to carcinoma in 88% of patients who were smokers over the age of 45 years. Bronchography features highly suggestive of carcinoma are reviewed and a “flooding technique”, which is described, is advocated in the performance of the examination. It is strongly recommended that bronchography precede bronchoscopy for this latter investigation to be fully effective.In the centres where bronchography has been widely employed in the assessment of bronchogenic carcinoma, the discovery of a blocked bronchus has been accorded great diagnostic significance. For example, one study of 1,408 bronchograms showed a blocked bronchus in 89% of 236 histologically proven lung cancers and only 3 false positive cases (Wiltet al.,1959). Similarly, in a review of 262 bronchograms a blocked bronchus was associated with bronchogenic carcinoma in 94.2% of a series which contained 97 proven cases of carcinoma (Rinkeret al.,1968).The first objective of this paper is to review the experience of the Royal Melbourne Hospital with the so‐called “block bronchus sign” over recent years and to assess its significance in the diagnosis of bronchogenic carcinoma.Furthermore, it has been pointed out that, whereas respiratory movement plays a large part in the filling of normal bronchi with contrast medium, a bronchus involved by carcinoma loses its flexibility and distensibility and:an fill only by gravity (Molnar and Riebel, 1964). In recognition of this assertion, a technique of bronchography in which the bronchi 3n the side of the lesion are flooded with contrast medium has been used for at least 10 years at the Royal Melbourne Hospital and a nigh degree of significance has been attached to the finding of a blocked bronchus (Hare and Bennett, 1962).The second objective of this paper is to evaluate the contribution made by the “flooding” technique o