Fine needle aspiration biopsy was done in 114 patients who showed mass like lesions in Chest, to get the cytologic diagnosis and pathogenic organism at Severance Hospital Yonsei Univ. The results were as follows : 1. Included 114 patients with 57 malignant tumors, 31 benign lesionsm, 18 pleural effusions and 8 unproven cases. 2. The most of patients were guided by ultrasound to approach the lesion but 18 patients by fluoroscopy due to the a bsence of the acoustic window. 3. In 57 proven cases with malignant tumor, the sensitivity of NAB was 86 %, but was 93% if suspicious cases were included. False negative cases were 2 lung cancers, 1 malignant fibrous histiocytoma and 1 pulmonary metastatic lesion. 4. In 31 cases with benign lesion, there was no case of false positive but specific benign diagnosis was got in 8(25.8%). 5. So the acurary of NAB indifferentiating benign and malignant lesion was 95.5%