Although clinical staging of neoplastic diseases has long remained the only approach to prognosis and treatment, parameters for stage determination, such as tumor size (T) and lymph-node involvement (N), do not always provide effective indication of optimal treatment. Molecular medicine has also provided useful indications as to an alternative and/or integration to clinical staging. Despite the numerous possibilities afforded by pre-operative staging techniques, failures in defining the real spread of neoplasias into surrounding structures have remained a very important diagnostic problem. The labeling of monoclonal antibodies binding with neoplastic target cells by way of radioactive isotopes introduced the techniques known as immunoscintigraphy and SPECT, which then evolved into radioimmunoguided surgery. Fourty patients suffering from colorectal cancer whose age ranged between 42-82 years were singled out for this study. Before undergoing surgery, they were administered pancoloscopy and macrobiopsies, AP-LL chest x-rays, hepatobiliary ECT, echoendoscopy, abdomen and pelvis CT with nephrostographic phase, and total body bone scintigraphy. They were treated with 125I-B72.3 and 125I-FO23C5 (5% and 95% of patients, respectively). Thyrosuppression was achieved by Lugol solution (15 drops x 3/die) from the 6th day before infusion and until the day of surgical operation. Radioimmunoguided surgery (RIGS) has also been tested on staging and second-look of ovarian tumors. Five years after surgical operation the survival rate of Dukes A patients (15%) was confirmed to amount to 100%, whereas for Dukes B patients (50%) having undergone RIGS-guided exeresis on single unrecognized metastases (2 patients) and on unrecognized n+ (5 patients) the survival rate was found to be 85% after 5 years; 2 patients deceased due to relapse; 1 patient deceased due to e.p.a. Finally, for Dukes C patients; (35%) having undergone RIGS-guided exeresis on unrecognized liver micrometastases (1 patient), on single isolated metastases (2 patients) and in the occurrence of multicentric lymph-node positivity (9 patients), the survival rate after 5 years was found to amount to 64%; 5 patients deceased due to relapse. Out of 19 patients without pre-operative evidence of ovarian tumor as opposed to just 1 patient suspected of pelvic recurrence, after intra-operative surgical radicalization (45%), 1 patient was diagnosed fibrosis (suspicious lesion on CT) and 1 other patient peritoneal MTS (negative CT) by means of RIGS. RIGS has made it possible: to localize primary and/or metastatic lesions; to determine tumor-free margins, loco-regional disease spread; to differentiate suspicious foci on inspection and palpation (biotopic sampling); to detect invisible and impalpable tumor foci (occult sites); to verify radical exeresis; to evaluate lymphatic drainage stations; to enable guided exeresis of liver metastases.