Caneer cells have several tumor-associated antigens on the cell surfaces, and antibodies against these antigens have been developed by many investigators. Radiolabeled antibodies have been used as new methods to diagnose and treat malignant tumors. Especially anti- carcinoembryonic antigen (CEA) is the most popular antibody for these purposes. In this investigation, we tried to label 131I and Tc-99m to anti-CEA monoclonal antibodies which were developed in the Seoul National University College of Medicine. We found CEA-79 and CEA-92 antibodies had the better immunological characteristics among 8 anti-CEA monoclonal antibodies. And radioiodination of CEA-79 could be performed by chloramine-T method, while radioiodination of CEA-92 by iodogen method. To label these antibodies with Tc-99m, we used pretargeting transchelation as direct labeling method. At first, Tc- 99m was bound to glucaric acid, and monoclonal antibody was reduced by β-mercaptoethanol. When these were incubated together, Tc -99m bound to glucarate was switched to monoclonal antibody because of higher affinity. We established conditions of several steps in this method. Anti-CEA monoclonal antibodies labeled with 131I and Tc-99m are expected to be used valuably in the detection and treatment of malignant tumors.