Thoracic computed tomography (CT) is an essential component in the preoperative staging of bronchial carcinomas as is mediastinoscopy (MSC) in cases of mediastinal lymphoma. It is known that endoscopic ultrasonography (EUS), as a new diagnostic procedure, can predict lymph-node involvement in cases of tumors in the upper gastrointestinal tract with an 80% probability. In a prospective study, we examined whether EUS could be used to ascertain the presence of mediastinal lymph nodes in cases of bronchial carcinoma. Since 1990, therefore, 32 patients with operable non-small-cell bronchial carcinoma have been examined with an Olympus-Aloka EU-M2 or EU-M3 (frequency 7.5 and 12 MHz) in addition to routine diagnostics. The graded cross-sections of lymph-node dissections obtained during subsequent surgery served as evidence as to the true or false prognosis of the lymph-node status. Endoscopic ultrasonography identifies the presence and estimates the size of subcarinal, tracheobronchial, paraortal and paraesophageal lymph nodes better than computed tomography. Lymph nodes lying behind organs containing air (pretracheal lymph nodes) cannot be identified by ultrasonography. Lymph-node involvement was correctly identified by EUS in 72% of the cases, and the specificity was 86%. The poor sensitivity, at 67%, is explained by the high proportion (37%) of patients with anthracosilicosis, as the latter produces the same echo pattern as malignant infiltration. In 47% of all the cases, CT showed enlarged mediastinal lymph nodes which were not actually infiltrated in 67%. Of these lymph nodes, 33% could be classified as definitely free of metastases on the strength of their echo pattern, the rest were inflamed or really infiltrated by metastases.(ABSTRACT TRUNCATED AT 250 WORDS)