A definitive diagnosis of pulmonary disease cannot be made, in a significant number of cases, without the employment of certain surgical procedures. A presumptive diagnosis may be reached with the aid of skin tests for tuberculosis, histoplasmosis, coccidioidomycosis, and blastomycosis, sputum smear and culture examinations for various organisms, fungal serological tests, and bronchoscopic study with cytologic and bacteriologic investigations of aspirated secretions as well as roentgenography. Not infrequently some of the positive results are not related to the disease under investigation and may lead to a false diagnosis and possibly misdirected therapy. A number of surgical procedures, aimed at diagnosis,18 have been employed in recent years in problem chest cases. These include lung biopsy, scalenus or paratracheal fat pad biopsy, pleural and pericardial biopsies, and exploratory thoracotomy. Today, these operations can be done with considerable safety as a result of improvements in the techniques of thoracic surgery, anesthesia, and pre- and post-operative management. The authors have employed lung biopsy when dealing primarily with diffuse pulmonary disease. Disseminated lung lesions caused by pneumoconiosis, tuberculosis, sarcoidosis, histoplasmosis, coccidioidomycosis, bIas