The role of radioimmunodetection in the detection of cancer has been established through the development of high affinity immunoconjugates and recent improvements in radiochemistry. Advances in imaging techniques, particularly single-photon emission computed tomography and image registration, also have dramatically improved the sensitivity and accuracy of tumor detection. Molecular engineering of immune constructs provides promise of enhanced tumor localization properties and reduced immunogenicity, allowing repeated studies to be performed. The role of radioimmunodetection in the evaluation of cancer patients will increase in importance in the future.