Stage-adjusted treatment of colorectal tumors requires precise knowledge of the extent of the underlying disease. Reliable staging is mandatory for intraoperative treatment planning. In this prospective trial monoclonal antibodies to CEA were labeled with 99mTc as tracer. Twenty patients were studied intraoperatively with a hand-held gamma detector. The results were compared to those obtained by all other diagnostic modalities and they were then confirmed by histopathology. Intraoperative scanning can reliably identify all tumor deposits and can confirm the radicality of the procedure. Thus, the use of immunoscintimetry is helpful in early decision making on adjuvant treatment modalities.