The results are presented of transthoracic, mainly fine-needle biopsies in 500 patients. The procedure was carried out under biplane fluoroscopic control. The overall accuracy was 89% in establishing malignancy for lung lesions (93% for lesions with a diameter greater than 20 mm and 71% for lesions less than 20 mm diameter). Biopsies were done on pleural lesions and mediastinal lesions with an accuracy of 76% and 83%, respectively. The complications were few: a pleural tube was needed in only 2% of the patients and one patient died. Inadequate material was attained from small peripheral lesions (diameter less than 20 mm) in 24% of the patients, so efforts should be made to improve the method in this respect.