Fifty patients with lung cancer underwent transesophageal endoscopic ultrasonography (EUS) for preoperative detection of metastases to the hilar and mediastinal lymph nodes. An electronic ultrasonic fiberscope with a linear array (EPB-503-FS, Machida-Toshiba) was used. Later, in surgery, a total of 513 nodes that could have been detected by EUS were removed. Of these, 54 nodes were found to be metastatic histologically, and 459 were non-metastatic. The rate of detection by EUS was 65% (35/54) for the metastatic nodes; the rate was 41% (186/459) for the non-metastatic nodes (p less than 0.01). Metastatic nodes were detected at high rates in every lymph node site. Non-metastatic nodes were detected at low rates in sites 1, 2, and 4, and at the highest rate in site 7. Metastatic nodes had characteristic internal echoes, affected by the extent of tumor and necrosis present in a node, and were detected more easily than non-metastatic nodes. For larger or rounder nodes, metastasis was more common (p less than 0.01). Lymph nodes that could be detected were classified into six types by their internal echo patterns; three of these types were rarely metastatic, and were called 'negative'; the other three were often metastatic, and were called 'positive'. In histological examinations, of the 'negative' nodes found in fact to be metastatic histologically, invasion by the tumor tended to be diffuse and necrosis was minute. The 'positive' nodes that were in fact metastatic tended to have one of two internal echo patterns (depending on the amount of necrosis) when invasion was diffuse, and a third pattern when invasion was localized.(ABSTRACT TRUNCATED AT 250 WORDS)