We reviewed 441 transthoracic needle aspiration biopsies to evaluate the use of the procedure in the diagnosis of pulmonary infections. Sixty-seven (15%) of the biopsies were performed because pulmonary infection was suspected. In these 67 cases, a specific diagnosis was made in 45 (67%). In 46 cases in which infection was ultimately found to be present, aspiration biopsy identified the organism in 35 (76%). Overall, clinically useful information was obtained in 54 (81%) of the 67 biopsies performed for pulmonary infection. In 369 biopsies performed for suspected malignant neoplasm, pulmonary infection was diagnosed in 13. The only significant complication was pneumothorax, which occurred in 18% of the biopsies. Chest tube placement was required in 5% of the biopsies. We conclude that transthoracic aspiration needle biopsy is of value in the diagnosis of suspected pulmonary infections.