The diagnosis for metastatic lymph nodes of lung cancer by the conventional CT is done only by the size of nodes, therefore, its diagnostic accuracy is questionable. For the purpose of more qualitative diagnosis in order to elevate accuracy of metastatic nodes, we studied a new CT image (Dynamic Thin Section CT) by combining the Thin Section CT with the Dynamic CT, and reviewed on the image of histopathological positive nodes. Firstly, for the preoperative cases of lung cancer, the conventional CT was performed for the whole chest with 10 mm-thickness and 10 mm-interval. Secondary, among them, the Dynamic CT by bolus-injection at the sites of detected hilar and mediastinal lymph nodes was performed. For this method, the Thin Section CT with 2 mm-thickness was used, and the image-detected nodes were isolated by surgery. We studied 25 cases whose images were compared with the histological findings. By the conventional CT sensitivity were 35.7%, specificity 54.5%, and accuracy 44.0%, in regarding the shorter diameter over 1 cm as positive nodes, then under diagnosis were 36%, over diagnosis 20%. Morphological features were reviewed on the image of metastatic lymph nodes in the Dynamic Thin Section CT, and were (1) lump-like lymph nodes, (2) disappearance of the fatty plane around the lymph nodes or uneven and irregular margins, (3) irregular internal structures of enhanced lymph nodes. Moreover, small lymph nodes were clearly detected, and the size was exactly measured.(ABSTRACT TRUNCATED AT 250 WORDS)