Based on a homogeneous series of 50 cases investigated within less than a week by CT scan and NMR imaging with mediastinoscopic correlation, and in 32 of theses cases with correlation with operative findings, a critical study was carried out of modern imaging methods for detection of mediastinal gland invasion from primary bronchial cancer. Axial mediastinoscopy presented absolute specificity and very high sensitivity (93%) markedly superior to those of CT scan and NMR imaging. The two latter examinations were practically of equal efficacy: sensitivity of NMR (80%) was somewhat higher than that of CT scan (70%) whereas specificity of CT scan was 83% as against 70% for NMR. Lack of efficacy of axial mediastinoscopy was in cases with extra-axial lymphatic extension (anterior mediastinal chains) from primary cancer. These results suggest that, in view of current inconveniences of NMR imaging, the best means for local and regional exploration of primary bronchial cancer preoperatively is combined CT scan and mediastinoscopy. The diagnosis of glandular enlargement of anterior mediastinal lymphatic chains should lead to performance of an anterolateral mediastinoscopy.