The authors report their experience in the radioimmunodetection of recurrent colorectal cancer in comparison with traditional examinations. 485 patients were studied after radical surgery for colorectal cancer: 168 (Group 1) were studied with a radioimmunoassisted follow-up plan including: Immunoscintigraphy (IS), serum markers assays, Radioimmunoguided Endoscopy (RIGE), Intraoperative Radioimmuno-localization (IORIL) in case of reoperation; 317 (Group 2) underwent a protocol with traditional examinations. In 24 patients of Group 1 IS was performed even at the time of their admission for primary cancer. 7 patients underwent RIGE for primary cancer and 16 in the follow-up. IORIL was performed in 12 patients with primary cancer and in 16 in the course of reoperation. The radioimmunodiagnostic methods were performed after a single administration of the radiolabeled MAb (111In F(ab')2 a-CEA and 111In B72.3). The radioimmunoassisted follow-up plan detected a greater number of recurrences than traditional examinations (27% vs 13%). The rates of radical reoperation in Group 1 and 2 were 61% and 37% respectively. 33% of the patients of Group 2 were alive 24 months after radical reoperation vs 62.5% of the patients of Group 1. Immunoscintigraphy demonstrated a good sensitivity and specificity, mainly in the detection of pelvic recurrences (sens. 92%, spec. 84%). The radioimmunoassisted follow-up plan was well accepted by the patients. RIGE led to the detection of 3 periluminal recurrences of rectal cancer that traditional investigations failed to demonstrate and in 5 cases influenced the patients management. IORIL detected minimal tumor foci (2 mm.) where pre and intraoperative study were negative, while the histopathologic examination gave evidence of tumor. Considering that the costs of the radioimmunodiagnostic methods and of traditional examinations are very similar, we can conclude that the radioimmunoassisted follow-up plan has a favorable cost/benefit rate and a remarkable impact on the treatment of patients with colorectal cancer.