Several therapeutic options are available for the treatment of rectal cancer. To determine the most appropriate method of treatment, Radioimmunoguided Surgery (RIGS) can be used as an intraoperative diagnostic tool and as an adjuvant to traditional methods for more accurate staging. RIGS employs radiolabeled monoclonal antibodies directed against tumor-associated antigens and a gamma-detection probe to discriminate between normal and abnormal tissue. Most patients with primary or recurrent rectal cancer are considered good candidates for surgery using RIGS scanning. Use of the RIGS system may result in improved patient survival through accurate assessment of extent of disease and the selection of appropriate therapy. Prospective studies are necessary to define the optimal use of this approach as an experimental and clinical tool.