To assess the place of bronchoscopy in the investigation of pleural effusion, 245 patients presenting during a two year period were reviewed. Of the 46 patients who had bronchoscopy, a positive yield was obtained in 13, though in five of these a second pleural aspiration was also diagnostic. Bronchoscopy was more likely to be diagnostic in patients presenting with a cough (12/24) than in those with no cough (1/22) (p less than 0.001), and in those whose chest X-ray revealed significant radiological abnormalities such as hilar enlargement, lung mass or persisting consolidation (12/29), than in those without such changes (1/17) (p less than 0.01). Bronchoscopy has a limited role in the investigation of pleural effusion. The presence or absence of cough, and the appearance of the chest X-ray, are both important considerations when planning the investigation of an undiagnosed pleural effusion.