The results of 88 transthoracic needle biopsies of lung lesions using the Rotex biopsy instrument are analyzed. Of 57 malignant lung lesions, 55 were diagnosed correctly. Two patients with false negative biopsies had technically inadequate examinations. All but one of the 28 benign lung lesions were correctly diagnosed as nonmalignant. One false positive diagnosis of malignancy was made. The occurrence of complications was similar to those reported for conventional fine needle aspiration. The high accuracy rate is attributed to the effectiveness of the Rotex instrument in sampling the lesions and to the use of biplane fluoroscopy.