During the past two decades, the in vivo application of monoclonal antibodies (MoAbs) in cancer diagnosis and therapy have been widely studied. This can be related to three main factors: (1) dramatic improvement in monoclonal antibody production, revolutionized by Kohler and Milstein; (2) improvement in radioisotopes and monoclonal antibody conjugation procedure and further simplification and ease of use of these procedures; and (3) the apparent safety of single or, in selected cases, multiple administration of MoAbs to humans. The development of radioimmunoscintigraphy or radioimmunodetection has added a significant new dimension to nuclear medicine imaging, and it is very likely to broaden our approach to diagnosis and perhaps therapy of malignant diseases. The indications and limitation of radioimmunoscintigraphy must be clearly outlined to the referring oncologists and surgeons. The unique capability of radiolabeled MoAbs in detecting occult disease, upstaging patients, and, most importantly, changing patient management must be emphasized. © 1993 W.B. Saunders Company. All rights reserved.