Fine-needle aspiration biopsy (FNAB) is a diagnostic method indicated in patients with pulmonary lesions that cannot be reached with a bronchoscope and when cytologic examinations of the sputum are persistently negative. Cells are aspirated under fluoroscopic control and stained using the Papanicolaou method for cytologic examination. Results are available within hours, and the material can be used for other studies. Between 1975 and 1984, the authors performed 845 FNABs in 342 patients. Diagnosis was established in 306 patients, or 89.5 per cent. Malignant neoplasm was diagnosed in 284 instances, benign disease in 22. In 176 patients with malignant tumors, the diagnosis was based on FNAB exclusively. In 108 patients who were operated on, the results of FNAB matched histology in 97 per cent. The aspiration specimen was inadequate in 36 patients, most of whom had diffuse lung disease. The incidence of complications was extremely low. FNAB is safe and reliable. It is recommended for use in clinical workup of undiagnosed pulmonary masses. FNAB enables rational planning of treatment when other diagnostic methods fail. The authors do not recommend FNAB for use in cases of diffuse pulmonary disease.