Radioimmunoguided surgery (RIGS) with radiolabeled monoclonal antibodies (MoAbs) has been reported as useful in second-look colorectal cancer procedures to improve surgical decision-making by helping avoid needless extensive surgery and expanding curative resection to sites of recurrence that have been missed previously. Sixteen asymptomatic patients with an history of colorectal cancer surgery underwent second-look surgery using the RIGS system, solely on the basis of rising serum levels of carcinoembryonic antigen (CEA). All patients were injected preoperatively with the anti-tumor-associated glycoprotein (TAG) 125I-labeled MoAb B72.3. Both traditional and RIGS exploration were used to determine the extension of a possible recurrence and its resectability for cure. Recurrent disease was observed in 14 of the 16 patients as the result of this combined exploration. Exploration alone showed the presence of recurrent disease in 9 of 16 patients (56.2%). Thus, RIGS found overlooked tumor in five patients (31.2%). All the additional RIGS-detected tumor sites were locoregional recurrences resectable for cure; conversely, no diagnostic improvements were shown in patients with liver metastases. Resection for cure was obtained by this approach in 9 of 16 patients (56.2%). Two patients without disease at the exploratory laparotomy recurred within 2 months at sites away from the abdomen. RIGS improved the results of colorectal cancer CEA-guided second-look procedures in asymptomatic patients by recruiting one-third of patients to curative resections.