Pleural aspergillosis occurs mostly in established cases of pleural empyema with a broncho-pleural fistula. Ten such patients are reported here: in all, Aspergillus fumigatus infection was related to tuberculosis. In three cases with an active, sputum-positive tuberculous process the pleural empyema was a complication of spontaneous pneumothorax in two, and of lung resection in one. In two cases the empyema occurred as a complication of tuberculous pleuritis, but A. fumigatus infection was noted only after the sputum had become negative for tubercle bacilli. In five patients with inactive tuberculosis, the empyema was a late com;plication of pneumothorax therapy. found in the sputum. A catheter was inserted into the pleural cavity, and Gram-negative bacilli sensitive to chloramphenicol were recovered from the pleural fluid. The patient was given a course of streptomycin, isoniazid, penicillin, and chloramphenicol therapy. In spite of this he deteriorated and after two months died of circulatory and respiratory failure. At necropsy both the adhesions and the pleura were covered by greenish fibrous masses which showed Aspergillus fumigatus on microscopical examination. In the apical posterior part of the visceral pleura an opening communication with the parenchymal lung cavity was found. Multiple tuberculous cavities were seen in both lungs.In this case the empyema resulted from perforation of the tuberculous cavity into the pleura. Secondary aspergillous infection of the empyema was not recognized during lifetime.