A significant number of monoclonal antibodies, suitable for in vivo management of carcinoma patients, have been recently developed and evaluated in clinical trials. They can be used successfully either for imaging or for radioimmunotherapy, although their clinical application shows advantages and limitations. With the advent of genetic engineering, it has become feasible to design molecules (i.e. chimeric and humanized antibodies, single-chain) to circumvent drawbacks or enhance a certain property. Several radionuclides can actually be used to be linked to monoclonal antibodies, including radiometallic isotopes which need bifunctional chelators. Coupling these radiometals to proteins will greatly increase diagnostic and therapeutic possibilities. The ability of radiolabeled monoclonal antibodies to localize tumors, markedly contributed to the development of a new intraoperative approach termed "Radioimmunoguided Surgery". This system, being used to better define tumor margin resection as well as occult tumor sites, is of importance in postoperative decision-making. Optimization of this technique is actually under evaluation at our Institution, especially in combination with Biological Response Modifiers.