Cytologic diagnosis of aspergillosis in cardiac transplantation. Fine-needle aspiration of the lung is now widely utilized to diagnose pulmonary neoplasms, but often serologic techniques or open-lung biopsy is relied on for the diagnosis of infectious pulmonary processes. We report a series of four patients in whom the fine-needle aspiration technique was used to make the rapid cytologic diagnosis of pulmonary aspergillosis. Culture confirmation was also obtained on the aspirated material. A discussion of the available techniques for the laboratory diagnosis of pulmonary aspergillosis is presented and the advantages of fine-needle aspiration cytology are stressed. Our favorable results support expanded use of fine-needle aspiration cytology in the evaluation of lung nodules appearing in immunosuppressed populations. 