In a pilot study, 21 patients underwent transbronchial fine needle aspiration (TBFNA) using a 45 cm-22 gauge needle guided by means of a semi-rigid metal sleeve, which was introduced through a standard rigid bronchoscope. A total of 33 aspirations were performed from main carina (15), paratracheal (five), and lobar carinal (13) foci. Six aspirations yielded malignant cellular samples, 22 aspirations presented only normal cells, and in five no adequate cellular sample was obtained. Fifteen patients underwent surgical exploration (mediastinoscopy with or without thoracotomy). Four of the cytologically malignant cases were explored and in three the aspiration site was confirmed histologically. In the remaining patients where the site of aspiration was explored, no tumour was demonstrated in the cytologically negative or cytologically inadequate cases. There were no complications from TBFNA. We suggest that TBFNA is useful in determining mediastinal malignant involvement rapidly and with lesser invasion than with current techniques.