In order to assess the value of nuclear magnetic imagery NMR in the diagnosis of the extent of bronchial cancers, 61 patients with operable bronchial carcinoma had both a CT scan and an NMR scan pre-operatively. Fifty one mediastinoscopies were performed. Twelve times there were mediastinal glandular enlargement. Ten times the thoracotomy was performed straight away. After pathological studies of the biopsy, 24 patients were N2, 25 N1, 12 N0; the sensibility of NMR to foresee lymph node invasions was 83% (specificity 70%), for CT scanning 75% (specificity 81%). Thirteen patients presented with a direct mediastinal or parietal invasion. The sensibility of detecting these invasions was only 38% for NMR (specificity 94.5%) and for CT scanning 54% (specificity 94.5%). There is little difference in the results and no statistical difference. This leads us to conclude that at present, NMR does not give more information than TDM in the diagnosis of operability in bronchial cancers.