Recurrences following resection for colorectal carcinoma occur in 50% of patients. Early detection and management of recurrences results in improved survival. Post-operative surveillance consists of serial CT scans, chest x-rays, colonoscopy and CEA determinations. Elevations in the serum CEA level can be the earliest and most sensitive indicator of recurrence. A rise in the serum CEA level in the absence of imageable disease presents a particular diagnostic challenge. Advanced imaging modalities such as Positron Emission Tomography (PET) and anti-CEA antibody immunoscintigraphy have been proposed as a way of localizing disease in these patients. This study will evaluate the sensitivity, specificity, accuracy and predictive value of FDG-PET scans and anti-CEA immunoscintigraphy in patients following resection of colorectal carcinoma who have rising serum CEA values in the absence of imageable disease by conventional modalities. Patients who meet inclusion criteria will undergo FDG-PET scan and anti-CEA immunoscintigraphy followed by an exploratory laparotomy. Abdominal explorations will be conducted by two surgeons, one of whom will be blinded to the results of the FDG-PET and CEA scans. All suspicious lesions will be biopsied and if possible resected. Results at operation will be correlated with the results of the scans. The goal of the study is to determine the role of FDG-PET scanning and anti-CEA immunoscintigraphy in the localization of recurrent colorectal carcinoma in patients with rising serum CEA levels.