Mediastinal lymph-node biopsy has been performed as a staging procedure in most cases of bronchogenic carcinoma since 1965. This study was carried out to assess the results of staging by this method in 75 patients. Biopsy sites were marked with hemoclips. Three zones were defined: zone 3 (inoperable), beyond the midline and above the lower border of the aortic arch; zone 1 (operable), more than 3 cm from the carcinoma, ipsilateral to the tumour; and zone 2, between zones 1 and 3. Forty of 75 patients had biopsy specimens showing carcinoma. The proportion was highest in small cell anaplastic carcinoma and lowest in squamous cell tumours. Of the 40 positive biopsies 35 were from zone 3. All the positive biopsy specimens showing small cell anaplastic carcinoma were from zone 3. Positive specimens correlated strongly with other evidence of inoperability. Mediastinal lymph-node biopsy is a definitive staging procedure.