This paper reviews the development of cancer imaging with radiolabeled antibodies to carcinoembryonic antigen and the current status and challenges for cancer therapy with radiolabeled antibodies. Advances in antibody preparations, choice of isotope and labeling methods, as well as imaging methods have resulted in rapid and sensitive radioimmunodetection agents that can affect the management of cancer patients. Radioimmunotherapy faces other problems, but advances in antibody engineering and control of dose-limiting myelotoxicity may result in reproducible clinical responses similar to the encouraging results being obtained in the radioimmunotherapy of lymphomas.