The sensitivity of a new tumor marker, TA 4-SCC, for lung tumors is examined and compared with the performance of the already established CEA. TA 4-SCC sensitivity is only moderate (30%), and it presents no significant differences among the various histologic types of lung cancer. In addition, unlike CEA, TA 4-SCC is present in large amounts in the serum of many stage I and II patients. In fact, its sensitivity in still curatively operable tumors reaches 30% compared to 10% with CEA.